General Science PYQs

The correct answer is increases.

Key Points

• In chemistry, the pH level of a solution is a measure of the molar concentration of hydrogen ions (H+) in the solution and as such is a measure of the acidity or basicity of the solution.
• When hydroxide ions (OH-) are added to an acidic solution, they react with the existing hydrogen ions (H+) to form water molecules (H2O). This chemical process is known as neutralization.
• The concentration of hydrogen ions (H+) decreases as they are consumed by the OH- ions. Since the pH scale is calculated as the negative logarithm of the H+ ion concentration (pH = -log[H+]), a reduction in H+ ions mathematically leads to a higher pH value. Hence, the statement that the pH increases is correct.
• An acidic solution typically has a pH value ranging from 0 to 6.9. As more OH- ions are introduced, the solution moves closer to pH 7.0, which is the neutral point on the scale.
• If the addition of OH- ions continues beyond the point of neutralization, the solution will eventually become basic (alkaline), resulting in a pH value greater than 7. Hence, the correct answer is increases.

Additional Information

• The pH Scale:
• The pH scale was introduced by the Danish biochemist S.P.L. Sorensen in the year 1909. It is used to express the acidity or alkalinity of a solution on a scale of 0 to 14.
• A pH of 7 represents a neutral solution, such as pure water at 25 degrees Celsius.
• Solutions with a pH less than 7 are considered acidic (e.g., gastric juice, lemon juice, and vinegar), while those with a pH greater than 7 are basic or alkaline (e.g., baking soda, milk of magnesia, and ammonia).
• Mathematical Relationship:
• The relationship between pH and pOH is defined by the equation pH + pOH = 14 at a temperature of 25 degrees Celsius.
• The ionic product of water (Kw) is a constant value of 1.0 x 10^-14 at standard temperature. This equilibrium ensures that as OH- concentration rises, the H+ concentration must fall proportionally.
• Logarithmic Nature:
• The pH scale is logarithmic, meaning each whole pH value below 7 is ten times more acidic than the next higher value. For example, a solution with pH 3 is 10 times more acidic than a solution with pH 4 and 100 times more acidic than a solution with pH 5.

Important Points

• Indicators and Measurement:
• The pH of a solution can be measured using litmus paper, universal indicators, or electronic pH meters. Blue litmus paper turns red under acidic conditions, while red litmus paper turns blue under basic conditions.
• Phenolphthalein is a common indicator that remains colorless in acidic solutions but turns pink when the solution becomes basic (around pH 8.2 to 10).
• Common pH Values:
• The pH of human blood is slightly basic, typically maintained within a narrow range of 7.35 to 7.45 for healthy physiological functioning.
• Acid rain usually has a pH value of less than 5.6, which can cause significant damage to aquatic ecosystems and limestone structures.
• Sodium Hydroxide (NaOH), a strong base, can have a pH as high as 14, whereas Hydrochloric Acid (HCl), a strong acid, can have a pH as low as 0.

The correct answer is Nephron.

Key Points

• The Nephron is the structural and functional unit of the kidney. It is essentially the basic filtration unit where the process of removing waste products from the blood occurs. Hence, option 1 is correct.
• Each human kidney contains approximately 1 million to 1.2 million nephrons, which work collectively to maintain the homeostatic balance of fluids and electrolytes in the body.
• A nephron is composed of two main parts: the Renal Corpuscle (which includes the Glomerulus and Bowman's capsule) and the Renal Tubule (comprising the Proximal Convoluted Tubule, Loop of Henle, and Distal Convoluted Tubule).
• The process of filtration begins in the Glomerulus, a tuft of capillaries where high blood pressure forces water and small solutes out of the blood and into the Bowman's capsule to form the filtrate.
• The primary function of the nephron is to filter blood, reabsorb useful substances like glucose and amino acids, and excrete nitrogenous wastes like urea and uric acid in the form of urine.

Additional Information

• Alveolus:
• These are tiny, balloon-shaped air sacs located at the end of the bronchial tubes in the lungs.
• They are the basic units of gas exchange in the respiratory system, where oxygen is diffused into the blood and carbon dioxide is removed. Hence, option 2 is incorrect.
• Tracheid:
• These are elongated, tube-like cells found in the xylem of vascular plants.
• Their main function is the conduction of water and minerals from the roots to the leaves and providing mechanical support to the plant. Hence, option 3 is incorrect.
• Villus:
• Villi are small, finger-like projections that line the inner wall of the small intestine.
• They serve to increase the surface area for the absorption of digested food into the bloodstream. Hence, option 4 is incorrect.

Important Points

• Excretory System in Humans: The system consists of a pair of kidneys, a pair of ureters, a urinary bladder, and a urethra.
• Ultrafiltration: This is the first step in urine formation, occurring under high pressure in the renal corpuscle. It filters out almost all constituents of the plasma except proteins.
• Selective Reabsorption: As the filtrate flows through the tubules, about 99% of the filtrate is reabsorbed by the renal tubules to prevent the loss of essential water and nutrients.
• Hormonal Regulation: The functioning of nephrons is regulated by hormones like Antidiuretic Hormone (ADH) or Vasopressin, which controls water reabsorption based on the body's hydration levels.
• Location: Kidneys are located toward the back of the abdominal cavity, one on each side of the spine, just below the rib cage.

The correct answer is A ceiling fan rotating at constant speed.

Key Points

• Uniform Circular Motion (UCM) is defined as the motion of an object traveling at a constant speed along a circular path. In this motion, while the speed remains the same, the direction of velocity changes continuously at every point.
• A ceiling fan rotating at a constant speed is a perfect example of this. Once the fan reaches its steady state (fixed speed setting), the tips of the blades describe a circular trajectory with a constant magnitude of velocity. Hence, statement 2 is correct.
• A person walking in a straight line represents rectilinear motion. Even if the speed is steady, it does not involve a circular path. Hence, statement 1 is incorrect.
• A bus accelerating on a straight road is an example of non-uniform linear motion. Since the bus is accelerating, its speed (magnitude of velocity) is changing over time. Hence, statement 3 is incorrect.
• A ball rolling down an inclined plane moves under the acceleration due to gravity. Its speed increases as it descends, meaning the motion is accelerated and not uniform. Hence, statement 4 is incorrect.

Additional Information

• Characteristics of Uniform Circular Motion:
• Speed: The magnitude of velocity remains constant throughout the motion.
• Velocity: It is a vector quantity. In UCM, the velocity is always tangential to the circular path. Because the direction changes at every instant, the velocity is not constant.
• Acceleration: Even though the speed is constant, the object is accelerating due to the change in direction. This is known as centripetal acceleration ($a_c = v^2/r$), which always points toward the center of the circle.
• Force: The net force causing this motion is the centripetal force ($F_c = mv^2/r$), which is required to keep an object moving in a circle.
• Angular Variables:
• Angular Displacement ($\theta$): The angle swept by the radius vector in a given time interval.
• Angular Velocity ($\omega$): The rate of change of angular displacement, typically measured in radians per second (rad/s). In UCM, $\omega$ is constant.
• The relationship between linear velocity (v) and angular velocity ($\omega$) is given by the formula $v = r \times \omega$, where r is the radius of the circle.

Important Points

• Real-world Examples of UCM:
• The motion of the hands of a clock (the tip of the second hand moves in UCM).
• A satellite orbiting the Earth in a perfectly circular orbit at a constant altitude and speed.
• An electron revolving around the nucleus in a circular orbit (in simplified atomic models).
• The rotation of the Earth on its axis (approximately uniform).
• Difference between Uniform and Non-Uniform Circular Motion:
• In Uniform Circular Motion, only the direction of velocity changes, while the speed remains constant.
• In Non-Uniform Circular Motion, both the direction and the magnitude (speed) of velocity change. For example, a fan being switched off or speeding up represents non-uniform circular motion.

The correct answer is 1 - d, 2 - c, 3 - b, 4 - a.

Key Points

• Calyx is the outermost whorl of a flower. Its individual units are called sepals. In most plants, sepals are green and leaf-like, serving the primary function of protecting the flower during the bud stage. Hence, 1 matches with d.
• Corolla is the second whorl of a flower, positioned internal to the calyx. It is composed of petals, which are usually brightly colored and often scented to attract pollinators like insects and birds. Hence, 2 matches with c.
• Androecium represents the male reproductive part of the flower. It consists of a collection of stamens. Each stamen is further divided into an anther (which produces pollen) and a filament (the supporting stalk). Hence, 3 matches with b.
• Gynoecium is the innermost whorl and serves as the female reproductive organ. It is made up of one or more carpels (also known as pistils). A typical carpel consists of an ovary, a style, and a stigma. Hence, 4 matches with a.

Additional Information

• Accessory Whorls: The calyx and corolla are considered accessory or non-essential whorls because they do not directly participate in the process of reproduction but assist in protection and attraction.
• Essential Whorls: The androecium and gynoecium are known as essential or reproductive whorls as they are directly responsible for the production of gametes and the formation of seeds.
• Complete and Incomplete Flowers: A complete flower is one that possesses all four whorls. If any one of these whorls is missing, it is categorized as an incomplete flower.
• Symmetry in Flowers: Flowers can be classified based on symmetry into actinomorphic (radial symmetry), zygomorphic (bilateral symmetry), or asymmetric (irregular).
• Perianth: In some flowers, like lilies, the calyx and corolla are not distinct and are collectively referred to as the perianth; the individual units of a perianth are called tepals.

Important Points

• Thalamus: The thalamus (or receptacle) is the swollen end of the pedicel (flower stalk) on which all the four floral whorls are arranged in a specific order.
• Stamen Structure: The anther is usually bilobed, and each lobe contains two pollen sacs (the microsporangia) where pollen grains are produced through meiosis.
• Carpel Structure: The ovary is the enlarged basal part containing ovules. The style is the elongated tube connecting the ovary to the stigma, which serves as the receptive platform for pollen grains during pollination.
• Monadelphous vs. Diadelphous: Stamens may be united in one bunch (monadelphous, e.g., China rose) or two bunches (diadelphous, e.g., pea).
• Apcocarpous vs. Syncarpous: If carpels are free, the condition is called apocarpous (e.g., lotus); if they are fused, it is called syncarpous (e.g., mustard).

The correct answer is 0 m/s.

Key Points

• When an object is dropped from a certain height, it is implicitly understood that the object starts its motion from a state of rest.
• In physics and kinematics, the initial velocity (represented by the symbol u) is the velocity of the object at the exact moment the observation of motion begins (at time t = 0).
• Since the object is simply released and not thrown or pushed with an external force, its initial velocity is exactly 0 m/s. Hence, the statement that the initial velocity is 0 m/s is correct.
• The moment the object is released, the force of gravity begins to act on it, causing it to accelerate downwards. However, this acceleration changes the velocity over time, meaning the speed is only zero at the very first instant.
• The value 9.8 m/s mentioned in the options is often confused with the acceleration due to gravity, but that value is measured in m/s², not m/s. Hence, option 2 is incorrect.

Additional Information

• Concept of Free Fall:
• An object is said to be in free fall when the only force acting upon it is gravity. In such cases, air resistance is often neglected in basic physics calculations.
• During free fall, all objects, regardless of their mass, accelerate toward the Earth at the same rate, which is approximately 9.8 m/s².
• Acceleration due to Gravity (g):
• The acceleration due to gravity is a constant vector pointing towards the center of the Earth. Its standard value is 9.80665 m/s², though it is frequently rounded to 9.8 m/s² or 10 m/s² for simplicity in exams.
• It is important to distinguish between velocity (speed in a direction) and acceleration (rate of change of velocity).
• Equations of Motion:
• For an object dropped from rest, the first equation of motion is v = u + gt. Since u = 0, the velocity at any time t becomes v = gt.
• The distance (height) fallen can be calculated using h = ut + ½gt². With u = 0, this simplifies to h = ½gt².

Important Points

• Dropped vs. Thrown: If the question stated the object was thrown downwards, the initial velocity would be a non-zero value (u > 0). If it is thrown upwards, the final velocity at the peak of its trajectory is 0 m/s.
• Terminal Velocity: In a real-world scenario with air resistance, a falling object eventually reaches a constant speed called terminal velocity, where the drag force equals the gravitational force.
• Frame of Reference: Usually, the downward direction is considered negative in coordinate systems. Thus, while the magnitude of the initial velocity is 0 m/s, the velocity as it falls would be represented with a negative sign (e.g., -9.8 m/s after 1 second).
• Location Variation: The value of g varies slightly depending on latitude and altitude. It is stronger at the poles and weaker at the equator due to the Earth's ellipsoid shape and rotation.

The correct answer is Different elements chemically bonded together.

Key Points

• A molecule of a compound is defined as a group of atoms belonging to two or more different elements that are chemically bonded together in a fixed ratio. Hence, statement 1 is correct.
• Metallic bonds occur between metal atoms of the same or different metals (forming alloys), but these structures are typically characterized as metallic lattices rather than discrete molecules of compounds. Hence, statement 2 is incorrect.
• The mixing of substances or ions without chemical bonding results in a mixture (homogeneous or heterogeneous), not a chemical compound, as compounds require a chemical reaction to form. Hence, statement 3 is incorrect.
• A substance composed of one type of atom only is an element. While homonuclear molecules like O2 or N2 exist, they are molecules of elements, not compounds, because they do not contain different elements. Hence, statement 4 is incorrect.
• In a compound, the constituent elements lose their individual physical and chemical properties, and the resulting molecule exhibits entirely new properties.

Additional Information

• Chemical Bonding: This is the physical process responsible for the attractive interactions between atoms and molecules. The primary types are Ionic Bonds (transfer of electrons) and Covalent Bonds (sharing of electrons).
• Law of Definite Proportions: Proposed by Joseph Proust in 1794, this chemical law states that a given chemical compound always contains its component elements in a fixed ratio by mass and does not depend on its source or method of preparation.
• Examples of Compounds:
• Water (H2O): Formed by two Hydrogen atoms and one Oxygen atom.
• Carbon Dioxide (CO2): Formed by one Carbon atom and two Oxygen atoms.
• Methane (CH4): A simple hydrocarbon compound consisting of one Carbon and four Hydrogen atoms.
• Molecular vs. Empirical Formula: The molecular formula shows the actual number of atoms of each element in a molecule, while the empirical formula shows the simplest whole-number ratio of atoms in a compound.

Important Points

• Valence Electrons: These are the electrons in the outermost shell of an atom that participate in the formation of chemical bonds. Atoms bond to achieve a stable electron configuration, often following the Octet Rule.
• Energy Changes: The formation of a compound from its elements is usually accompanied by the evolution or absorption of energy in the form of heat, light, or electricity.
• Separation: Unlike mixtures, the elements in a compound cannot be separated by physical methods like filtration or distillation; they can only be separated by chemical or electrochemical reactions.
• Molar Mass: Each compound has a specific molar mass, which is the sum of the atomic masses of all the atoms present in its chemical formula.

The correct answer is They need currents of widely different values to operate properly.

Key Points

• In a series circuit, the electric current remains the same through all components connected in the loop. This means the current (I) flowing through the electric bulb is identical to the current flowing through the electric heater.
• An electric bulb and an electric heater have significantly different power ratings. A typical household bulb may consume 40W to 100W, while a heater typically consumes 1000W to 2000W.
• Because of these different power requirements, they require currents of widely different values to function at their rated capacity. For instance, at 220V, a 100W bulb requires approximately 0.45 Amperes, whereas a 2000W heater requires nearly 9 Amperes. Hence, statement 2 is correct.
• In a series connection, if the current is high enough to operate the heater, it will instantly burn out the filament of the bulb. Conversely, if the current is low enough for the bulb, the heater will not generate any noticeable heat.
• The total voltage in a series circuit is divided among the components proportional to their resistance (V = V1 + V2). It does not decrease to zero. Hence, statement 1 is incorrect.
• The total equivalent resistance in a series circuit is the sum of individual resistances (Rs = R1 + R2). It is never zero unless the components themselves have no resistance. Hence, statement 3 is incorrect.
• The current does not stop immediately unless the circuit is broken (e.g., the bulb blows out); it simply flows at a sub-optimal level for the high-power device. Hence, statement 4 is incorrect.

Additional Information

• Ohm's Law: This fundamental principle states that V = IR, where V is voltage, I is current, and R is resistance. In series circuits, the high resistance of a bulb limits the total current of the entire circuit, making it insufficient for the heater.
• Resistance of Appliances: Since P = V²/R, for a constant voltage, a high-power device like a heater has low resistance, while a low-power device like a bulb has high resistance.
• Parallel Circuits: This is the standard for domestic wiring. In a parallel circuit, the voltage across each appliance is the same (e.g., 220V in India), allowing each device to draw the current it needs independently based on its own resistance.
• Power Consumption: The formula P = I²R shows that heat produced depends on the square of the current. In series, the limited current caused by the bulb's high resistance results in negligible power output for the heater.

Important Points

• Single Point of Failure: One major disadvantage of series circuits is that if one component (like the bulb) fuses or is switched off, the entire circuit is broken, and all other components (like the heater) stop working.
• Voltage Division: In a series arrangement, the component with the highest resistance (the bulb) takes the maximum voltage drop, leaving very little voltage for the heater to operate.
• Practical Application: Series circuits are rarely used for appliances but are common in decorative string lights (fairy lights), where many small bulbs of the same rating are used together.
• Safety: Connecting high-load appliances in series with low-load ones can lead to overheating of wires or short circuits if the bulb's holder or filament cannot handle the potential current surge.

The correct answer is Increase in concentration of harmful substances at higher trophic levels.

Key Points

• Biological magnification, also referred to as biomagnification, is the process characterized by the progressive increase in the concentration of toxic substances (such as heavy metals or persistent organic pollutants) at each successive trophic level of a food chain. Hence, statement 1 is correct.
• These harmful substances are typically non-biodegradable, meaning they cannot be broken down by the metabolism of organisms or environmental decomposers. Consequently, they accumulate in the tissues of living beings.
• The process is not defined by an increase in biological activities like metabolic rates or reproduction, but specifically by the chemical load per unit of biomass. Hence, statement 2 is incorrect.
• Pollutants involved in biomagnification are resistant to being broken down by decomposers (like bacteria and fungi); their persistence in the environment is what allows them to enter the food web and accumulate. Hence, statement 3 is incorrect.
• In any ecosystem, according to the 10 percent law of energy transfer, energy decreases as it flows from producers to higher consumers, whereas the concentration of toxins increases. Hence, statement 4 is incorrect.

Additional Information

• Common Pollutants: The most frequent chemicals associated with this phenomenon include DDT (Dichlorodiphenyltrichloroethane), Mercury, Arsenic, Lead, and Polychlorinated biphenyls (PCBs).
• DDT and Wildlife: A classic example occurred in the 20^th century when DDT usage led to the thinning of eggshells in predatory birds like Bald Eagles and Peregrine Falcons, causing their populations to crash until the chemical was banned in 1972 in the United States.
• Human Health Risks: Humans often occupy the highest trophic level. Consumption of contaminated fish can lead to Mercury poisoning, famously known as Minamata Disease, first discovered in 1956 in Japan.
• Lipid Solubility: Most biomagnifying substances are lipophilic (fat-soluble). This means they dissolve in fats and oils within an organism's body, making them difficult to excrete through water-based systems like urine.

Important Points

• Bioaccumulation vs. Biomagnification: It is important to distinguish these terms. Bioaccumulation occurs within a single organism over its lifespan, while biomagnification describes the increase across the entire food chain.
• Trophic Level Concentration: In an aquatic ecosystem, the concentration of DDT might start at 0.000003 ppm (parts per million) in water, reach 0.04 ppm in zooplankton, 0.5 ppm in small fish, 2 ppm in large fish, and finally 25 ppm in fish-eating birds.
• Global Regulation: The Stockholm Convention on Persistent Organic Pollutants (POPs), adopted in 2001, is an international environmental treaty that aims to eliminate or restrict the production and use of substances that undergo biomagnification.

The correct answer is AgNO3 + NaCl → AgCl + NaNO3.

Key Points

• A Double Displacement Reaction (also known as a metathesis reaction) is a type of chemical process where two compounds react, and the positive ions (cations) and the negative ions (anions) of the two reactants switch places, forming two new compounds.
• In the equation AgNO₃ + NaCl → AgCl + NaNO₃, the silver ion (Ag⁺) from Silver Nitrate swaps its nitrate partner for the chloride ion (Cl^-) from Sodium Chloride. Similarly, the Sodium (Na⁺) ion joins with the Nitrate (NO₃^-) ion. Hence, statement 2 is correct.
• The general representation of this reaction is AB + CD → AD + CB. It typically occurs in aqueous solutions where the ions are free to move and interact.
• The reaction between Silver Nitrate and Sodium Chloride is a classic example of a precipitation reaction, which is a sub-type of double displacement. It results in the formation of Silver Chloride (AgCl), which is an insoluble white precipitate.
• In contrast, 2Mg + O₂ → 2MgO represents two elements combining to form a single compound, which is a Combination Reaction. Hence, statement 1 is incorrect.
• The reaction Zn + CuSO₄ → ZnSO₄ + Cu shows a single element (Zinc) replacing another (Copper) in a compound. This is a Single Displacement Reaction. Hence, statement 3 is incorrect.
• The process CaCO₃ → CaO + CO₂ involves a single reactant breaking down into two products upon heating. This is a Decomposition Reaction. Hence, statement 4 is incorrect.

Additional Information

• Types of Double Displacement Reactions:
• Precipitation Reaction: This occurs when two aqueous solutions react to form an insoluble solid called a precipitate. The reaction AgNO₃ + NaCl is the most common example found in laboratory chemistry.
• Neutralization Reaction: This occurs between an Acid and a Base to form Salt and Water. For example, HCl + NaOH → NaCl + H₂O is a double displacement reaction where H⁺ and Na⁺ ions exchange partners.
• Chemical Reaction Characteristics:
• Combination Reaction: Characterized by the formation of a single product from two or more reactants. An example is the burning of coal or the synthesis of water from hydrogen and oxygen.
• Decomposition Reaction: The opposite of combination. It requires energy in the form of Heat (Thermal), Light (Photolytic), or Electricity (Electrolytic) to break chemical bonds. The electrolysis of water is a famous 1800s discovery using this principle.
• Displacement Reaction: Governed by the Reactivity Series. A more reactive metal (like Zinc or Iron) will displace a less reactive metal (like Copper) from its salt solution.

Important Points

• Solubility Rules: To predict if a double displacement reaction will result in a precipitation, scientists use solubility rules. For instance, most Nitrates (NO₃^-) are soluble, while Silver Chloride is notably insoluble in water.
• Oxidation State: Unlike Redox reactions (Single Displacement or Combination), the oxidation states of the atoms in a double displacement reaction usually remain unchanged. The ions simply switch partners without a net transfer of electrons.
• Applications: These reactions are widely used in water treatment to remove harmful ions, in the manufacture of pigments, and in qualitative inorganic analysis to identify unknown ions in a sample.

The correct answer is H2O.

Key Points

• A molecule of a compound is defined as a substance formed by the chemical combination of two or more different types of elements in a fixed proportion by mass.
• H2O (Water) is composed of two hydrogen atoms and one oxygen atom. Since it contains different elements chemically bonded together, it is a molecule of a compound. Hence, option 2 is correct.
• N2 (Nitrogen) consists of two atoms of the same element (Nitrogen) bonded together. It is classified as a homoatomic molecule or a molecule of an element. Hence, option 1 is incorrect.
• He (Helium) is a noble gas and exists as a single atom (monoatomic). It does not naturally form molecules with other atoms under standard conditions and is considered an element in its simplest form. Hence, option 3 is incorrect.
• O2 (Oxygen) is a diatomic molecule consisting of two oxygen atoms. Because the atoms are of the same element, it represents a molecule of an element rather than a compound. Hence, option 4 is incorrect.

Additional Information

• Elements: These are pure substances that consist of only one type of atom. They cannot be broken down into simpler substances by ordinary chemical reactions. Examples include Carbon (C), Iron (Fe), and Gold (Au). There are currently 118 recognized elements in the Periodic Table.
• Compounds: A compound is a substance where atoms of different elements are held together by chemical bonds (ionic or covalent). The properties of a compound are distinct from the properties of the individual elements that compose it. For instance, Sodium (Na) is a reactive metal and Chlorine (Cl) is a toxic gas, but together they form Sodium Chloride (NaCl), which is edible table salt.
• Molecules: A molecule is the smallest unit of a substance that retains the chemical properties of that substance. It can be homoatomic (like O3 or P4) or heteroatomic (like CO2 or CH4).
• Chemical Formula: This notation represents the ratio of atoms in a substance. In H2O, the numerical subscript 2 indicates there are two hydrogen atoms for every one oxygen atom.
• Atomicity: This refers to the total number of atoms present in one molecule of an element or compound. For example, H2O has an atomicity of 3 (2 Hydrogen + 1 Oxygen).

Important Points

• Law of Definite Proportions: Established by Joseph Proust in 1799, this law states that a chemical compound always contains its constituent elements in a fixed ratio by mass, regardless of how the compound was prepared.
• Noble Gases: Elements like Helium (He), Neon (Ne), and Argon (Ar) are chemically inert and usually exist as single atoms. They are known as monoatomic elements.
• Diatomic Elements: There are seven elements that naturally exist as diatomic molecules (molecules of two atoms) in their gaseous state: Hydrogen (H2), Nitrogen (N2), Oxygen (O2), Fluorine (F2), Chlorine (Cl2), Bromine (Br2), and Iodine (I2).
• Valency: The combining capacity of an atom is called its valency. It determines how many chemical bonds an atom can form to create a molecule or compound. For example, Oxygen has a valency of 2, while Hydrogen has a valency of 1, leading to the formation of H2O.

The correct answer is Oviduct (fallopian tube).

Key Points

• Fertilisation is the biological process where a male gamete (sperm) fuses with a female gamete (ovum or egg) to form a zygote. In the human female reproductive system, this event specifically occurs in the Oviduct, also known as the Fallopian tube.
• The fallopian tubes are a pair of long, narrow ducts that connect the ovaries to the uterus. They are approximately 10 to 12 cm in length.
• During ovulation, a mature egg is released from the ovary and is swept into the fallopian tube by finger-like projections called fimbriae.
• Fertilisation usually takes place in the widest section of the fallopian tube, called the ampulla. The sperm cells must swim through the vagina, cervix, and uterus to reach the egg in the oviduct. Hence, the statement regarding the oviduct as the site of fertilisation is correct.
• Once fertilisation occurs, the resulting zygote remains in the fallopian tube for about 3 to 4 days, undergoing rapid cell division as it moves toward the uterus.

Additional Information

• Ovary:
• The ovaries are the primary female reproductive organs located on either side of the lower abdomen.
• Their main functions are oogenesis (the production of eggs) and the secretion of essential hormones like estrogen and progesterone. Fertilisation does not happen here.
• Uterus (Womb):
• The uterus is a hollow, pear-shaped organ where a fertilised egg implants and develops into a fetus.
• The process of the embryo attaching to the uterine wall is called implantation, which typically occurs about 6 to 9 days after fertilisation. If fertilisation does not occur, the uterine lining (endometrium) is shed during menstruation.
• Cervix:
• The cervix is the lower, narrow portion of the uterus that opens into the vagina.
• It acts as a gateway that allows sperm to enter the uterus and serves as the birth canal during delivery. It also produces cervical mucus that changes in consistency throughout the menstrual cycle to facilitate or inhibit sperm movement.
• Zygote to Embryo:
• After the sperm penetrates the egg, the diploid zygote is formed. It undergoes cleavage (mitotic divisions) to become a morula and then a blastocyst before reaching the uterus for gestation.

The correct answer is Red blood corpuscles.

Key Points

• Red blood corpuscles (RBCs), also known as erythrocytes, are the primary medium for oxygen transportation in the blood of vertebrates. Hence, the correct answer is Red blood corpuscles.
• These cells contain a specialized red-colored, iron-containing complex protein called haemoglobin. Approximately 97% of oxygen is transported by RBCs in the blood, while the remaining 3% is carried in a dissolved state through the plasma.
• When blood passes through the lungs, oxygen binds to the iron atoms in haemoglobin to form a temporary and reversible compound known as oxyhaemoglobin. Each molecule of haemoglobin can carry a maximum of four molecules of oxygen.
• Upon reaching the peripheral tissues where the partial pressure of oxygen is low, oxyhaemoglobin dissociates, releasing the oxygen for cellular respiration.
• Mature human RBCs are biconcave in shape and lack a nucleus (enucleated). This unique structure increases the surface area for gas exchange and provides more internal space to accommodate haemoglobin.

Additional Information

• White blood corpuscles (WBCs):
• Also known as leucocytes, these cells are part of the body's immune system.
• Their primary function is to fight infections and protect the body against foreign pathogens like bacteria and viruses.
• Unlike RBCs, they contain a nucleus but do not contain haemoglobin, which is why they are colorless.
• Blood platelets:
• Scientifically called thrombocytes, these are cell fragments produced from megakaryocytes in the bone marrow.
• They play a critical role in blood clotting (coagulation). When a blood vessel is injured, platelets aggregate at the site to form a plug, preventing excessive blood loss.
• A significant reduction in platelet count can lead to clotting disorders and internal bleeding.
• Lymph:
• Lymph is a colorless fluid that circulates through the lymphatic system.
• It is derived from interstitial fluid and contains specialized WBCs called lymphocytes.
• Its functions include draining excess fluid from tissues, transporting fats absorbed from the intestine, and acting as a filter for pathogens in the lymph nodes.

Important Points

• The average life span of a human red blood cell is approximately 120 days.
• The process of formation of RBCs is called erythropoiesis, which primarily occurs in the red bone marrow in adults.
• Worn-out or damaged RBCs are destroyed in the spleen, which is often referred to as the "graveyard of RBCs".
• The red color of blood is attributed specifically to the haeme group (iron-porphyrin complex) within the haemoglobin protein.
• The transport of carbon dioxide is also managed by blood, where about 20-25% is carried by haemoglobin as carbamino-haemoglobin, and the majority (about 70%) is transported as bicarbonate ions.

The correct answer is To provide maximum green matter for fodder.

Key Points

• Fodder crops are specifically cultivated to provide nutritious feed for livestock such as cattle, goats, and sheep. The primary objective is to obtain the highest possible vegetative biomass.
• Tallness in these plants ensures a greater volume of stems, while profuse branching leads to an increased number of leaves. Together, these traits result in maximum green matter per unit area. Hence, statement 1 is correct.
• A higher leaf-to-stem ratio, often achieved through branching, is desirable because leaves are generally more digestible and contain higher crude protein levels than stems.
• Reducing harvesting time is not a primary reason for seeking tall or branched plants; in fact, very tall and branched crops might require more effort to harvest and process. Hence, statement 2 is incorrect.
• While grain yield is important for food crops, fodder crops are often harvested before they reach the reproductive stage (flowering and seed setting) to ensure the greens remain succulent and palatable. Hence, statement 3 is incorrect.
• Improving soil fertility is a secondary benefit of certain fodder crops (like legumes), but the physical traits of height and branching are selected specifically for animal consumption needs. Hence, statement 4 is incorrect.

Additional Information

• Types of Fodder Crops:
• Kharif Fodder: Crops like Sorghum (Jowar), Maize, and Bajra are grown during the monsoon season. They are known for their rapid growth and high biomass.
• Rabi Fodder: Berseem (Egyptian Clover) and Oats are popular winter fodder crops. Berseem is particularly valued for its multiple cuttings and high protein content.
• Desirable Agronomic Traits:
• In cereal crops like Wheat, scientists prefer dwarf varieties to prevent lodging (bending of the stalk). However, in fodder crops, the "Gigantism" trait is preferred to maximize the feed available for Animal Husbandry.
• Palatability: The green matter must be soft and easy for animals to chew, which is why they are often harvested during the vegetative phase.
• Nutritional Quality:
• Fodder crops provide essential minerals, vitamins, and fiber. Leguminous fodder such as Lucerne (Alfalfa) and Cowpea helps in nitrogen fixation, which enriches the soil with Nitrogen while providing high-quality feed.

Important Points

• Crop Improvement: In plant breeding for fodder, the selection criteria differ from food grains. Breeders look for multi-cut genotypes that can regenerate quickly after being harvested.
• Economic Impact: Efficient fodder production is crucial for the Dairy Industry in India. Since land availability for grazing is shrinking, high-yielding tall and branched varieties help meet the nutritional requirements of a large livestock population.
• Silage and Hay: Tall fodder crops with high dry matter content are ideal for making Silage (preserved green fodder) to be used during the lean season.

The correct answer is same mass number but different atomic number.

Key Points

• Isobars are atoms of different chemical elements that possess the same mass number (A) but have different atomic numbers (Z). Hence, option 1 is correct.
• The mass number is the total count of nucleons, which includes both protons and neutrons located in the atomic nucleus.
• Because isobars have different atomic numbers, they represent different chemical elements and occupy different positions in the Periodic Table.
• A classic example of isobars includes Argon (Ar), Potassium (K), and Calcium (Ca), all of which can have a mass number of 40, while their atomic numbers are 18, 19, and 20 respectively.
• Atoms that share the same atomic number but have different mass numbers are classified as isotopes. Hence, option 2 is incorrect.
• Properties like melting point and refractive index are specific physical and optical characteristics of substances and are not used to define or categorize atomic species such as isobars. Hence, options 3 and 4 are incorrect.

Additional Information

• Isotopes:
• These are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number.
• All isotopes of a given element have the same number of protons in each atom.
• Example: Hydrogen-1 (Protium), Hydrogen-2 (Deuterium), and Hydrogen-3 (Tritium) are the three isotopes of hydrogen.
• Isotones:
• These are atoms of different elements that have the same number of neutrons but different atomic numbers and mass numbers.
• Example: Carbon-14 (6 protons, 8 neutrons) and Oxygen-16 (8 protons, 8 neutrons) are isotones.
• Nuclear Isomers:
• These are atoms with the same atomic number and the same mass number but exist in different energy states within the nucleus.
• They are usually represented by the letter m (for metastable) after the mass number, such as Technetium-99m.
• Chemical and Physical Properties:
• Isobars exhibit completely different chemical properties because their electron configurations (determined by the atomic number) are different.
• Their physical properties also differ significantly as they belong to different elements with varying densities and structures.

Important Points

• Etymology: The term isobar was first suggested by Alfred Walter Stewart in 1918. It is derived from the Greek words isos (equal) and baros (weight).
• Beta Decay: In nuclear physics, isobars are frequently produced during Beta decay. When a nucleus undergoes Beta-minus decay, a neutron is converted into a proton. This increases the atomic number by 1 but the mass number remains unchanged, creating an isobar of the original element.
• Identification: Isobars can be distinguished using Mass Spectrometry, although their mass differences are extremely small (equal to the mass difference between a neutron and a proton-electron pair).
• Stability: According to Mattauch's isobar rule, if two adjacent elements on the Periodic Table have isotopes of the same mass number, at least one of them must be radioactive.

The correct answer is 12 N.

Key Points

• To find the magnitude of the applied force, we use Newton’s Second Law of Motion, which states that the force acting on an object is equal to the mass of the object multiplied by its acceleration (F = m × a).
• The given parameters in the problem are: Mass (m) = 4 kg, Initial Velocity (u) = 2 m/s, Final Velocity (v) = 8 m/s, and Time (t) = 2 s.
• First, we must calculate the acceleration (a) of the object. Acceleration is defined as the rate of change of velocity over time. The formula is a = (v - u) / t.
• Substituting the values into the acceleration formula: a = (8 m/s - 2 m/s) / 2 s. This results in a = 6 / 2 = 3 m/s². Hence, the acceleration of the object is 3 m/s².
• Once the acceleration is known, we apply Newton's Second Law: Force (F) = mass (m) × acceleration (a).
• Calculation: F = 4 kg × 3 m/s² = 12 N. Therefore, the magnitude of the applied force is 12 N, which makes statement 4 the correct answer.

Additional Information

• Newton’s Second Law of Motion:
• This law defines Force quantitatively. It establishes that the acceleration of an object depends on two variables: the net force acting upon the object and the mass of the object.
• The law can also be stated in terms of momentum (p): The applied force is equal to the rate of change of momentum (F = dp/dt).
• In the SI system, the unit of force is the Newton (N), named after Sir Isaac Newton. One Newton is defined as the force required to accelerate 1 kg of mass at 1 m/s².
• Kinematics and Dynamics:
• The relationship used to find acceleration (v = u + at) is one of the equations of motion for constant acceleration.
• Mass is a measure of inertia, which is the tendency of an object to resist changes in its state of motion. In this problem, the 4 kg mass requires a specific amount of force to overcome its inertia and reach the higher velocity.
• Velocity is a vector quantity, meaning it has both magnitude and direction. Since the velocity increases from 2 m/s to 8 m/s in the same direction, the force is applied in the direction of motion.

Important Points

• Impulse: The product of force and time is known as impulse. In this case, Impulse = F × t = 12 N × 2 s = 24 N·s. Impulse is also equal to the change in momentum (Δp = m(v - u) = 4 × 6 = 24 kg·m/s).
• Constant Force: The problem specifies a constant force, which implies uniform acceleration. If the force were variable, the acceleration would not be constant, and simple kinematic equations would require integration.
• Dimensional Analysis: Force has the dimensions of [M L T²]. Ensuring units are consistent (kg, m, s) is vital to obtaining the result in Newtons.

The correct answer is They alter the hormone levels to inhibit ovulation and uterus preparation.

Key Points

• Chemical methods of birth control, primarily known as hormonal contraceptives, work by interfering with the body's natural reproductive cycle using synthetic hormones like progestogen or a combination of progestogen and estrogen.
• These hormones act on the pituitary gland to inhibit the secretion of Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH), which are essential for ovulation. Without the surge of these hormones, the ovaries do not release an egg. Hence, statement 1 is correct.
• In addition to preventing ovulation, chemical methods alter the quality of the endometrium (the lining of the uterus), making it thin and unreceptive for the implantation of a fertilized egg. Hence, statement 1 is correct.
• Chemical methods do not "promote" ovulation; instead, they maintain a steady level of hormones to trick the body into thinking it is already pregnant or to bypass the mid-cycle hormonal peak. Hence, statement 2 is incorrect.
• While some hormonal methods thicken the cervical mucus to prevent sperm transport, they do not "thicken the vaginal wall" to block entry. Hence, statement 3 is incorrect.
• Mechanical blocking of the fallopian tubes is a surgical method (Permanent method) known as Tubectomy, not a chemical one. Chemical methods generally do not aim to suppress menstruation entirely, though they may lighten the flow. Hence, statement 4 is incorrect.

Additional Information

• Oral Contraceptive Pills (OCPs):
• These are popular chemical methods taken orally. A famous example in India is Saheli, a non-steroidal oral pill developed by the Central Drug Research Institute (CDRI) in Lucknow.
• Unlike traditional pills that are taken daily, Saheli is a 'once-a-week' pill with very few side effects and a high contraceptive value.
• Intrauterine Devices (IUDs):
• These are devices inserted by doctors in the uterus through the vagina. They are categorized into non-medicated IUDs (e.g., Lippes loop), copper-releasing IUDs (e.g., CuT, Cu7, Multiload 375), and hormone-releasing IUDs (e.g., Progestasert, LNG-20).
• Hormone-releasing IUDs make the uterus unsuitable for implantation and the cervix hostile to the sperm.
• Barrier Methods:
• These prevent the physical meeting of ovum and sperm. Common examples include condoms, diaphragms, cervical caps, and vaults. Condoms also provide the additional benefit of protecting against STIs and AIDS.
• Surgical Methods (Sterilization):
• These are terminal methods to prevent any more pregnancies. In males, the procedure is called Vasectomy (small part of the vas deferens is removed or tied up). In females, it is Tubectomy (small part of the fallopian tube is removed or tied up).

Important Points

• Medical Termination of Pregnancy (MTP): Voluntary termination of pregnancy before full term is known as MTP or induced abortion. The Government of India legalized MTP in 1971 with strict conditions to avoid its misuse (like female foeticide).
• Family Planning Program: India was one of the first countries in the world to initiate action plans and programs at a national level to attain total reproductive health as a social goal. These programs, called 'Family Planning', were initiated in 1951.
• Emergency Contraceptives: Administration of progestogens or progestogen-estrogen combinations within 72 hours of coitus have been found to be very effective as emergency contraceptives to avoid possible pregnancy due to rape or casual unprotected intercourse.

The correct answer is Pressure = Thrust ÷ Area.

Key Points

• Pressure is defined as the physical force exerted on an object per unit area. It is the ratio of thrust to the area over which that force is distributed.
• The mathematical formula for pressure is Pressure = Thrust / Area. This indicates that pressure is directly proportional to the magnitude of the thrust and inversely proportional to the surface area. Hence, the formula Pressure = Thrust ÷ Area is correct.
• Thrust is the total force acting perpendicularly on a surface. It is measured in Newtons (N).
• If the area is kept constant, an increase in thrust will lead to an increase in pressure. Conversely, if the thrust is kept constant, decreasing the area will significantly increase the pressure.
• This principle explains why a sharp needle (small area) can easily penetrate a surface compared to a blunt object (large area) when the same amount of force is applied.

Additional Information

• SI Unit: The standard unit of pressure is the Pascal (Pa), named after the French scientist Blaise Pascal. One Pascal is equal to one Newton per square meter (1 N/m²).
• Scalar Quantity: Pressure is a scalar quantity because it does not have a specific direction of its own, even though the force (thrust) acting on the surface is a vector quantity.
• Atmospheric Pressure: This is the pressure exerted by the weight of the atmosphere. At sea level, the standard atmospheric pressure is approximately 101,325 Pa or 1 atm.
• Applications in Daily Life:
• School Bags: They are provided with broad straps to increase the surface area, thereby reducing the pressure on the shoulders of the student.
• Tools: Cutting tools like knives and axes have very thin edges to reduce the area and maximize the pressure, allowing them to cut through materials easily.
• Foundations: The foundations of high-rise buildings are made wide to distribute the heavy weight (thrust) over a larger area, preventing the building from sinking into the ground.

Important Points

• Fluid Pressure: In liquids and gases, pressure acts in all directions. The pressure in a liquid increases with depth due to the weight of the liquid column above it. The formula for fluid pressure is P = h × d × g, where h is height, d is density, and g is acceleration due to gravity.
• Conversion Units: Apart from Pascal, other common units for pressure include bar, torr, and pounds per square inch (psi). For example, 1 bar is equal to 100,000 Pa.
• Relationship Summary:
• Higher Thrust + Same Area = Higher Pressure.
• Same Thrust + Smaller Area = Higher Pressure.
• Same Thrust + Larger Area = Lower Pressure.

The correct answer is 5 s.

Key Points

• The motion of the particle is a case of uniformly accelerated motion in a straight line, where the rate of change of velocity remains constant over time.
• The initial velocity (u) of the particle is given as 5 m/s, which is its speed at the start of the measured interval.
• The final velocity (v) reached by the particle is 15 m/s, indicating an increase in speed due to acceleration.
• The uniform acceleration (a) is specified as 2 m/s². This value represents that the particle's velocity increases by 2 meters per second for every one second of motion.
• To determine the time (t) taken for this change, we use the first equation of motion: v = u + at. By substituting the known values into the equation, we get 15 = 5 + (2 × t).
• Solving for t involves subtracting the initial velocity from the final velocity (15 - 5 = 10) and then dividing by the acceleration (10 / 2), resulting in 5 seconds. Hence, the correct option is 5 s.

Additional Information

• Equations of Motion: These equations, often attributed to the work of Sir Isaac Newton and Galileo, describe the relationship between displacement (s), velocity (v and u), acceleration (a), and time (t).
• First Equation: v = u + at (defines the velocity-time relationship).
• Second Equation: s = ut + 1/2 at² (defines the displacement-time relationship).
• Third Equation: v² = u² + 2as (defines the velocity-displacement relationship).
• Uniform Acceleration: This occurs when an object's velocity changes at a constant rate. In a velocity-time graph, uniform acceleration is represented by a straight line, and the slope of this line gives the numerical value of the acceleration.
• SI Units: In the International System of Units, velocity is measured in m/s (meters per second), acceleration in m/s² (meters per second squared), and time in s (seconds).
• Vector Nature: Both velocity and acceleration are vector quantities, meaning they possess both magnitude and direction. If the acceleration is in the opposite direction of the velocity, it is called retardation or deceleration.

Important Points

• Displacement Calculation: Using the time calculated (5 s), the displacement of the particle during this interval can also be found using the second equation of motion: s = (5 × 5) + 0.5 × 2 × (5²) = 25 + 25 = 50 meters.
• Average Velocity: For uniformly accelerated motion, the average velocity can be calculated as (u + v) / 2. In this case, (5 + 15) / 2 = 10 m/s. Multiplying this by the time (10 m/s × 5 s) also gives the displacement of 50 meters.
• Historical Context: The study of kinematics was revolutionized in the 17^th century. Understanding these basic principles is essential for engineering, astrophysics, and mechanical design applications.

The correct answer is Particles of suspension do not scatter a beam of light.

Key Points

• A suspension is defined as a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium. Hence, statement 2 is correct.
• The particles of a suspension are quite large, typically with a diameter greater than 1000 nanometers (or 1 micrometer). Due to this size, the particles are visible to the naked eye without the aid of a microscope. Hence, statement 3 is correct.
• Particles of a suspension scatter a beam of light passing through it, making the path of light visible. This phenomenon is known as the Tyndall Effect. Therefore, the claim that they do not scatter light is factually incorrect. It is important to note that if the suspension is left to stand and the particles settle, the mixture will no longer scatter light. Hence, statement 1 is incorrect.
• Due to their relatively large size, the particles of a suspension can be easily separated from the mixture by the physical process of filtration. When passed through a filter paper, the solid particles are trapped as residue while the liquid passes through. Hence, statement 4 is correct.
• A suspension is inherently unstable. If left undisturbed, the particles will eventually settle down at the bottom of the container due to the force of gravity.

Additional Information

• Types of Mixtures based on Particle Size:
• True Solution: A homogeneous mixture where the particle size is less than 1 nanometer (10⁻⁹ m). These particles do not scatter light and cannot be separated by filtration. An example is salt dissolved in water.
• Colloid: A heterogeneous mixture (though often appearing homogeneous) with particle sizes between 1 nm and 1000 nm. They show the Tyndall Effect but the particles do not settle down. Examples include milk, fog, and blood.
• Physical State of Suspension: In a typical suspension, the dispersed phase is a solid, while the dispersion medium can be a liquid or a gas.
• Common Examples: Some well-known examples of suspensions include chalk powder in water, muddy water, flour in water, and Milk of Magnesia (Magnesium hydroxide).
• Settling and Optical Properties: When the particles in a suspension settle (a process called sedimentation), the mixture loses its ability to scatter light because the large particles are no longer distributed throughout the medium to intercept the light beam.

Important Points

• Tyndall Effect: Named after the scientist John Tyndall, who first studied it in 1869. It is a critical test to distinguish between a true solution and a colloid or suspension.
• Separation Methods: While filtration works for suspensions, colloids require more specialized techniques like centrifugation because their particles pass through standard filter papers.
• Stability Comparison: True solutions are the most stable, followed by colloids, while suspensions are the least stable mixtures as they undergo phase separation over time.

The correct answer is CH₄(g) + 2O₂ → CO₂(g) + 2H₂O.

Key Points

• Exothermic reactions are chemical reactions that release energy to the surroundings, usually in the form of heat or light. In these reactions, the total energy of the products is less than the total energy of the reactants.
• The reaction CH₄(g) + 2O₂ → CO₂(g) + 2H₂O represents the combustion of methane (the primary component of natural gas). This process releases a significant amount of thermal energy, making it a classic example of an exothermic reaction. Hence, statement 1 is correct.
• The reaction 2AgCl(s) → 2Ag(s) + Cl₂(g) occurs in the presence of sunlight. It is a photochemical decomposition reaction where energy is absorbed from light to break the chemical bonds. Such reactions are endothermic. Hence, statement 2 is incorrect.
• The reaction CaCO₃(s) → CaO(s) + CO₂(g) is the thermal decomposition of calcium carbonate. This reaction requires the absorption of heat (energy) to proceed, classifying it as an endothermic reaction. Hence, statement 3 is incorrect.
• The reaction Pb(s) + CuCl₂(aq) → PbCl₂(aq) + Cu(s) is a single displacement reaction. In this reaction, the more reactive lead (Pb) displaces the less reactive copper (Cu) from its salt solution. It is not categorized as a primary example of an exothermic combination reaction. Hence, statement 4 is incorrect.

Additional Information

• Combination Reaction: This is a type of reaction where two or more reactants combine to form a single product. A common example is the burning of magnesium ribbon in air (2Mg + O₂ → 2MgO), which is also exothermic.
• Respiration: It is a vital biological process considered an exothermic reaction. During respiration, glucose (C₆H₁₂O₆) reacts with oxygen in the cells of our body to produce carbon dioxide, water, and energy.
• Endothermic Reaction: These reactions are the opposite of exothermic reactions, as they absorb energy from their surroundings. Most decomposition reactions (breaking down a compound) are endothermic because they require energy in the form of heat, light, or electricity.
• Enthalpy Change (ΔH): In chemistry, exothermic reactions are characterized by a negative enthalpy change (-ΔH), while endothermic reactions have a positive enthalpy change (+ΔH).

Important Points

• Practical Examples: Common exothermic processes include the decomposition of vegetable matter into compost and the neutralization reaction between an acid and a base.
• Activation Energy: Even exothermic reactions like the combustion of methane require an initial spark or activation energy to begin, but once started, they release enough energy to sustain the reaction.
• Photosynthesis: Unlike respiration, photosynthesis in plants is an endothermic process because it requires the absorption of solar energy to convert carbon dioxide and water into food.