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The correct answer is Boiling point of a liquid increases with an increase in atmospheric pressure and decreases with a decrease in atmospheric pressure..

Key Points

• The boiling point of a liquid is defined as the temperature at which its vapor pressure equals the external atmospheric pressure surrounding the liquid.
• At high altitudes, such as hill stations, the atmospheric pressure is significantly lower than at sea level due to the thinner air column above. Because the external pressure is lower, water requires less heat to match its vapor pressure with the environment, causing it to boil at temperatures below 100°C.
• In a pressure cooker, the steam produced is trapped inside a sealed container, which rapidly increases the internal pressure. This elevated pressure prevents water molecules from escaping into the gas phase until a much higher temperature is reached, typically around 120°C.
• The physical principle involved is that the boiling point is directly proportional to the external pressure; as pressure increases, more thermal energy is needed to facilitate the phase change from liquid to gas.

 Additional Information

• Vapor Pressure:
• It is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases at a given temperature in a closed system.
• As temperature increases, the kinetic energy of molecules increases, thereby increasing the vapor pressure.
• Clausius-Clapeyron Equation:
• This equation characterizes the phase transition between two states of matter and mathematically relates the dependence of boiling point on pressure.
• Practical Implications:
• In mountainous regions, food takes longer to cook in open vessels because the water cannot exceed its low boiling point (e.g., 92°C), providing less heat to the food.
• Autoclaves used in hospitals for sterilization operate on the same principle as a pressure cooker to reach temperatures high enough to kill resistant bacteria and spores.

The correct answer is Larger pressure.

Key Points

• Pressure is defined as the thrust acting perpendicularly per unit area of a surface.
• The mathematical relationship between these physical quantities is expressed by the formula: Pressure = Thrust / Area.
• According to this formula, pressure is inversely proportional to the area on which the force (thrust) acts, provided the magnitude of the force remains constant.
• Therefore, if a force acts on a smaller area, the pressure generated is larger because the force is concentrated over a limited space.
• In contrast, if the same force acts on a larger area, the pressure becomes smaller as the force is distributed across a wider surface.

 Additional Information

• Concept of Thrust:
• Thrust is the total perpendicular force exerted by an object on a surface.
• The SI unit for thrust is the Newton (N), the same as for any other force.
• Units of Pressure:
• The SI unit of pressure is the Pascal (Pa), where 1 Pa = 1 N/m².
• It is named in honor of the French mathematician and physicist Blaise Pascal.
• Real-World Applications:
• Sharp Tools: Needles, nails, and knives have pointed or sharp edges to reduce the contact area, thereby exerting larger pressure to penetrate surfaces easily.
• Broad Foundations: High-rise buildings and dams have very wide bases to increase the area and reduce the pressure exerted on the ground to prevent sinking.
• Heavy Vehicles: Tractors and tanks use wide tires or caterpillar tracks to distribute weight over a larger area, minimizing pressure on soft ground.

The correct answer is Against gravity.

Key Points

• Gravitational Potential Energy (GPE) is the energy an object possesses due to its position in a gravitational field, typically relative to the Earth's surface.
• To lift an object of mass m to a height h, an external force must be applied to counteract the object's weight. The weight of an object is the downward force exerted by gravity, calculated as Weight = m × g, where g is the acceleration due to gravity (approximately 9.8 m/s²).
• Work is mathematically defined as the product of force and displacement. When lifting an object, the displacement is upward, while the gravitational force acts downward.
• Because the lifting force acts in the opposite direction to the gravitational pull, the process is described as doing work against gravity.
• This work done is stored in the object as potential energy, expressed by the formula U = mgh. If no other forces (like friction) are present and the object is moved at a constant velocity, the work performed by the external agent exactly equals the gain in Potential Energy.

 Additional Information

• Conservative Forces and Paths:
• Gravity is a conservative force, which means the work done to move an object between two points is independent of the path taken. Whether the object is lifted vertically or along a curved path, the GPE depends only on the vertical displacement.
• Direction of Movement:
• If an object moves in the direction of gravity (falls downward), the potential energy is converted into kinetic energy, and the work done by gravity is positive while the GPE decreases.
• Work-Energy Theorem:
• According to this principle, the total work done on an object is equal to its change in Kinetic Energy. When lifting an object with constant velocity, there is no change in kinetic energy, so the external work done against gravity translates entirely into potential energy.

The correct answer is The atmosphere bends the starlight due to gradual changes in refractive index.

Key Points

• This phenomenon occurs due to Atmospheric Refraction, which is the deviation of light from a straight line as it passes through the Earth's atmosphere.
• As starlight enters the atmosphere, it travels from a vacuum (rarer medium) into layers of air with increasing density (denser medium).
• The refractive index of the Earth's atmosphere gradually increases as we move closer to the surface because the air becomes denser near the ground.
• According to the laws of refraction, when light travels from a rarer to a denser medium, it bends towards the normal. Since the atmosphere consists of layers with varying indices, the light bends continuously.
• The human eye perceives light as traveling in a straight line. Therefore, when we trace the refracted ray backward, the apparent position of the star appears slightly higher than its actual position, especially when observed near the horizon.

 Additional Information

• Atmospheric Refraction Effects:
• Advanced Sunrise and Delayed Sunset: The Sun is visible to us about 2 minutes before the actual sunrise and 2 minutes after the actual sunset due to the same bending of light.
• Twinkling of Stars: The stars act as point sources of light. As the physical conditions of the atmosphere change, the refractive index fluctuates, causing the apparent position and intensity of light to change, resulting in a twinkling effect.
• Apparent Flattening of the Sun: At sunrise and sunset, the bottom part of the Sun's disc is closer to the horizon and refracted more than the upper part, making the Sun appear oval or flattened.
• Refractive Index: It is the ratio of the speed of light in a vacuum to the speed of light in a specific medium. For air at sea level, the refractive index is approximately 1.00029.

The correct answer is Weeds compete with crops for resources.

Key Points

• Weeds are defined as undesirable and unwanted plants that grow alongside cultivated crops, often possessing more aggressive growth characteristics than the main crop.
• The primary reason for weed management is that these plants engage in interspecific competition for vital limiting resources, specifically soil nutrients (nitrogen, phosphorus, potassium), irrigation water, sunlight, and physical space.
• Since weeds consume the fertilizers and moisture intended for the crops, their presence leads to nutrient deficiency, causing stunted growth and a significant reduction in the overall crop yield.
• Uncontrolled weed growth can harbor pests and pathogens, further indirectly damaging the health of the primary agricultural produce.
• Managing weeds early in the crop life cycle is critical to ensuring that the crop establishes a canopy and utilizes available resources efficiently for biomass production.

 Additional Information

• Common Weed Examples:
• Xanthium (Gokhroo), Parthenium (Gajar ghas), and Cyperinus rotundus (Motha) are some of the most prevalent weeds found in Indian agriculture.
• Control Strategies:
• Mechanical Methods: Includes uprooting weeds by hand, ploughing, and using tools like the khurpi for weeding.
• Chemical Methods: The application of herbicides or weedicides, such as 2,4-D, Atrazine, and Butachlor, which are designed to selectively eliminate weeds.
• Biological Control: Utilizing natural enemies like insects or specific bio-herbicides to suppress the growth of specific weed species.
• Cultural Methods: Practicing crop rotation, intercropping, and timely sowing of seeds to provide the crop a competitive advantage over weeds.

The correct answer is Both statements I and II are true..

Key Points

• Evaporation is the process of a liquid changing into a gas or vapour at any temperature below its boiling point. It differs from boiling as it is a surface phenomenon, where only the particles at the surface gain enough kinetic energy to break the forces of attraction and escape. Hence, statement I is correct.
• The rate of evaporation depends heavily on the amount of surface area exposed to the atmosphere. Because evaporation is a surface-based process, increasing the area allows a larger number of molecules to transition from the liquid phase to the vapour phase simultaneously. Hence, statement II is correct.

 Additional Information

• Several other physical factors influence the evaporation rate in a given environment:
• Temperature: An increase in temperature provides more thermal energy to the particles, increasing their kinetic energy and speeding up the conversion to vapour.
• Humidity: This refers to the concentration of water vapour in the air. High humidity levels decrease the evaporation rate because the air is already saturated and cannot easily absorb more moisture.
• Wind Speed: Increased wind speed moves the water vapour away from the liquid surface immediately after it forms, preventing local saturation and thus increasing the rate of evaporation.
• Evaporative Cooling: During evaporation, the liquid absorbs the latent heat of vaporization from the surroundings or the remaining liquid, which results in a cooling effect.

The correct answer is The ovary develops into a fruit while the ovule becomes a seed.

Key Points

• In Angiosperms, the process of fertilization triggers a series of developmental changes where the flower transforms into a fruit containing seeds.
• The ovule, which contains the embryo sac, undergoes structural changes post-fertilization to develop into the seed. This seed houses the embryo and often a food-storing tissue called the endosperm.
• The ovary matures and ripens into the fruit. The primary biological function of the fruit is to protect the developing seeds and facilitate their dispersal through various agents like wind, water, or animals.
• During this transition, most accessory floral parts, including the petals, stamens, style, and stigma, typically wither and fall off as their reproductive roles are completed.

 Additional Information

• The transformation of floral parts involves specific cellular differentiations:
• Zygote: The diploid cell formed by the fusion of a male gamete and an egg cell develops into the embryo.
• Integuments: The outer protective layers of the ovule harden to form the seed coat, consisting of the testa (outer) and tegmen (inner).
• Ovary Wall: This tissue develops into the pericarp, which is the wall of the fruit. In fleshy fruits, the pericarp differentiates into the exocarp, mesocarp, and endocarp.
• Triple Fusion: The fusion of the second male gamete with two polar nuclei results in the Primary Endosperm Nucleus (PEN), which develops into the nutrient-rich endosperm.
• Persistent Calyx: While most sepals fall off, in certain plants like brinjal and tomato, the calyx remains attached even after the fruit matures.

The correct answer is They have the same number of protons..

Key Points

• Isobars are defined as atoms of different chemical elements that possess the same mass number (A) but different atomic numbers (Z). Hence, statement 1 is correct.
• Since the atomic number represents the number of protons in a nucleus and determines the identity of an element, isobars must have a different number of protons by definition. Hence, statement 2 is incorrect.
• The mass number is the total sum of protons and neutrons; because isobars have the same total sum but different proton counts, the number of neutrons in their nuclei must vary to maintain the constant mass sum. Hence, statement 3 is correct.
• Chemical properties are governed by the electronic configuration, which depends on the atomic number; because isobars belong to different elements with different atomic numbers, they exhibit distinct chemical behaviors. Hence, statement 4 is correct.

 Additional Information

• Isotopes:
• These are atoms of the same element having the same atomic number but different mass numbers.
• Example: Protium, Deuterium, and Tritium are isotopes of Hydrogen.
• Isotones:
• These are atoms of different elements that contain the same number of neutrons.
• Example: Carbon-14 (6 protons, 8 neutrons) and Oxygen-16 (8 protons, 8 neutrons).
• Isobar Examples:
• Argon-40 (₁₈Ar⁴⁰) and Calcium-40 (₂₀Ca⁴⁰) are classic examples of isobars, where both share a nucleon count of 40.
• Physical properties like density and boiling points often differ significantly between isobars due to their distinct elemental identities.

The correct answer is Transport of water and food.

Key Points

• Complex permanent tissues are composed of more than one type of cell that work together as a unit to perform a common specialized function.
• The primary function of these tissues is the conduction or transport of materials throughout the plant body, which is why they are also termed vascular tissues.
• Xylem is the complex tissue responsible for the unidirectional transport of water and dissolved minerals from the roots to the aerial parts of the plant. It consists of tracheids, vessels, xylem parenchyma, and xylem fibers.
• Phloem is the complex tissue that facilitates the translocation of organic food (mainly sucrose) from the leaves (source) to storage organs and growing regions (sink) in a bidirectional manner. It comprises sieve tubes, companion cells, phloem parenchyma, and phloem fibers.
• Together, Xylem and Phloem constitute the vascular bundles, which are essential for the survival of plants in terrestrial environments by ensuring efficient resource distribution.

 Additional Information

• Protection of plant body:
• This is the function of protective tissues like the Epidermis and Cork (Phellem).
• The Epidermis protects against water loss, mechanical injury, and invasion by parasitic fungi.
• Storage of food:
• This is primarily performed by simple permanent tissues, specifically Parenchyma.
• Parenchyma cells are thin-walled and have large vacuoles to store starch, fats, and water.
• Photosynthesis:
• This occurs in Chlorenchyma, which is a specialized type of parenchyma containing chloroplasts.
• It is predominantly found in the mesophyll layer of leaves.

The correct answer is Maximum at center.

Key Points

• The magnetic field (B) at any point on the axis of a circular current-carrying loop is always directed along the axis of the loop, passing through its center.
• The magnitude of the magnetic field at a distance x from the center of a loop with radius R and current I is given by the formula: \( B = \frac{\mu_0 I R^2}{2(R^2 + x^2)^{3/2}} \). This field reaches its maximum value at the center of the loop where x = 0, simplifying to \( B = \frac{\mu_0 I}{2R} \).
• The magnetic force (F) acting on a charged particle with charge q moving with velocity (v) is determined by the Lorentz Force equation: F = q(v × B), or F = qvB sin(θ) in scalar form.
• As the particle moves perpendicular to the axis, the angle θ between the velocity vector and the magnetic field vector is 90°. Since sin(90°) = 1, the force magnitude becomes F = qvB.
• Because the magnetic field strength is greatest at the center of the loop and decreases as one moves away along the axis, the deflecting force experienced by the particle is also maximum at the center.

 Additional Information

• Lorentz Force Properties:
• The magnetic force is always perpendicular to the plane containing the velocity and magnetic field vectors.
• Since the force is perpendicular to motion, the work done by the magnetic field on the charge is zero, and the kinetic energy remains constant.
• Biot-Savart Law:
• This fundamental law relates magnetic fields to the magnitude, direction, and proximity of the electric current.
• It establishes that the field intensity is inversely proportional to the square of the distance from the source element.
• Directional Rules:
• The Right-Hand Thumb Rule is used to find the direction of the magnetic field produced by the current loop.
• Fleming’s Left-Hand Rule can be used to determine the direction of the magnetic force acting on a positive charge.