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The correct answer is Speedometers.

Key Points

• Archimedes' Principle states that when a body is immersed fully or partially in a fluid, it experiences an upward buoyant force that is equal to the weight of the fluid displaced by it.
• Speedometers are instruments designed to measure and display the instantaneous speed of a vehicle. They typically function using Eddy currents, magnetic sensors, or GPS technology and do not rely on fluid displacement or buoyancy.
• Lactometers are used to determine the purity of milk by measuring its density. Since the instrument floats at different levels based on the fluid's weight and displacement, it is a direct application of Archimedes' Principle.
• Hydrometers are devices used to measure the specific gravity or relative density of liquids. They operate by observing the depth to which a calibrated glass tube sinks in a liquid, which is governed by the upward thrust of the displaced fluid.
• The Designing of submarines and ships heavily relies on this principle to ensure stability and buoyancy. Submarines specifically utilize ballast tanks to alter their weight by taking in or discharging water, allowing them to submerge or surface by manipulating the displaced volume.

 Additional Information

• Buoyant Force:
• It is the upward force exerted by a fluid on an object.
• The magnitude of this force is calculated as the product of the density of the fluid, the acceleration due to gravity, and the volume of the displaced fluid.
• Specific Gravity:
• It is a dimensionless quantity representing the ratio of the density of a substance to the density of pure water at 4 degrees Celsius.
• Instruments like Hydrometers use this ratio to identify the composition of various liquids like battery acid or antifreeze.
• Eddy Current Mechanism:
• Found in traditional speedometers, where a rotating magnet creates a magnetic field that induces currents in a non-ferrous metal cup, creating torque without physical contact.

The correct answer is CuSO4 and AgNO3 only.

Key Points

• Chemical reactions between a metal and a salt solution depend on the Reactivity Series, where a more reactive metal displaces a less reactive metal from its compound.
• Zinc (Zn) is positioned higher than Copper (Cu) in the reactivity series. When Zinc metal is added to CuSO₄, a displacement reaction occurs, forming Zinc Sulphate and solid Copper.
• Zinc is significantly more reactive than Silver (Ag). Consequently, Zinc reacts with AgNO₃ to displace Silver, resulting in the formation of Zinc Nitrate and metallic Silver deposits.
• Magnesium (Mg) is located above Zinc in the reactivity series, making it more reactive. Therefore, Zinc cannot displace Magnesium from the MgSO₄ solution, and no reaction occurs.
• Adding Zinc to a ZnSO₄ solution results in no observable chemical change because a metal does not react with its own salt solution to produce a new substance.

 Additional Information

• Reactivity Gradient: The metals involved follow the reactivity order: Magnesium (Mg) > Zinc (Zn) > Copper (Cu) > Silver (Ag).
• Magnesium: An alkaline earth metal that is highly electropositive.
• Zinc: A transition metal often used in galvanization and as a reducing agent in chemical labs.
• Copper and Silver: These are noble-like metals found lower in the series, making them easily displaced by Zinc.
• Visual Indicators:
• The Blue vitriol (CuSO₄) solution loses its blue color as Cu²⁺ ions are reduced to Copper metal.
• Displacement of Silver from Silver Nitrate typically results in a lustrous grey or silver precipitate on the surface of the Zinc strip.
• Standard Reduction Potential: Zinc has a standard reduction potential of −0.76 V, which is lower than Copper (+0.34 V) and Silver (+0.80 V), allowing it to act as the anode or reducing agent in these specific redox pairs.

The correct answer is To increase groundwater by storing rainwater.

Key Points

• A check-dam is a small, often temporary, barrier constructed across a drainage ditch, swale, or channel to lower the velocity of flow.
• The primary objective of these structures is to promote groundwater recharge. By slowing down the surface runoff, the dam creates a small pool that allows water to percolate through the soil layers into the underground aquifers.
• In arid and semi-arid regions, check-dams serve as a vital tool for water harvesting, ensuring that rainwater is not lost as flash floods but is instead stored beneath the surface for future irrigation needs.
• These structures significantly reduce soil erosion by trapping sediments and silt, which would otherwise be carried away by fast-moving water, thus preserving the fertility of the land.
• By maintaining a higher water table, check-dams ensure that nearby borewells and open wells remain functional even during the dry summer months.

 Additional Information

• Watershed Management:
• Check-dams are a core component of integrated watershed management, which aims to conserve every drop of rain within a specific geographical area.
• They can be constructed using various materials such as boulders, gabions (wire cages filled with rocks), logs, or reinforced concrete.
• Environmental Impact:
• Unlike large-scale dams, check-dams have a minimal ecological footprint and do not involve large-scale displacement of local populations.
• They improve soil moisture content, which directly benefits the growth of natural vegetation and crops in the immediate vicinity.
• Siltation control provided by these dams prevents the clogging of larger downstream reservoirs and riverbeds.

The correct answer is Double.

Key Points

• The Weight of an object is defined as the gravitational force with which a celestial body, such as the Earth, attracts the object toward its center.
• Mathematically, weight is expressed by the formula W = m × g, where m represents the mass of the object and g represents the acceleration due to gravity.
• This equation indicates that weight is directly proportional to the mass of the object when the gravitational acceleration remains constant.
• If the mass is doubled (2m) and g is kept constant, the new weight (W_new) becomes (2m) × g, which is equivalent to 2W.
• Consequently, any linear change in mass results in an identical linear change in weight, provided the gravitational field strength does not fluctuate.

 Additional Information

• Mass:
• It is a scalar quantity that measures the inertia or the total quantity of matter within a body.
• The SI unit of mass is the kilogram (kg), and it remains constant regardless of the object's location in the universe.
• Weight:
• It is a vector quantity because it has a specific direction, which is always towards the center of the planet.
• The SI unit of weight is the Newton (N).
• Unlike mass, weight varies depending on the value of g; for instance, an object's weight on the Moon is approximately 1/6^th of its weight on Earth due to the Moon's weaker gravity.
• Acceleration due to Gravity (g):
• On the surface of the Earth, its standard value is taken as 9.8 m/s².
• It reaches its maximum at the poles and its minimum at the equator, and becomes zero at the center of the Earth.

The correct answer is C₃H₈.

• Alkanes have the general molecular formula C_nH_2n+2. The molecular mass of the alkane can be calculated using the atomic masses of carbon (12 u) and hydrogen (1 u).

Key Points

• For propane (C₃H₈), molecular mass = (3 × 12) + (8 × 1) = 36 + 8 = 44 u.
• Therefore, the alkane having molecular mass 44 is C₃H₈ (Propane).
• Propane is the third member of the alkane homologous series.
• Alkanes are saturated hydrocarbons containing only single covalent bonds between carbon atoms.

Additional Information

• Methane (CH₄)
• First member of the alkane series.
• Molecular mass = 12 + 4 = 16 u.
• Ethane (C₂H₆)
• Second member of the alkane series.
• Molecular mass = (2 × 12) + (6 × 1) = 30 u.
• Propane (C₃H₈)
• Third member of the alkane series.
• Molecular mass = 44 u.
• Commonly used as LPG fuel.
• Butane (C₄H₁₀)
• Fourth member of the alkane series.
• Molecular mass = (4 × 12) + (10 × 1) = 58 u.
• Alkanes
• General formula: C_nH_2n+2.
• Known as saturated hydrocarbons because they contain only single bonds.
• Major constituents of natural gas and petroleum.

The correct answer is Locate underwater objects.

Key Points

• SONAR is an acronym for Sound Navigation and Ranging. It is a sophisticated device that utilizes ultrasonic waves to determine the distance, direction, and speed of underwater objects such as submarines, icebergs, or sunken ships.
• The system typically comprises a transmitter and a detector mounted on the hull of a vessel. The transmitter emits high-frequency ultrasound waves that travel through the water medium.
• When these waves encounter an object or the seabed, they are reflected back as echoes. These reflected waves are captured by the detector, which converts the acoustic energy into electrical signals for processing.
• The distance to the object is calculated using the formula 2d = v × t, where 'd' is the distance, 'v' is the speed of sound in water, and 't' is the total time interval between the transmission and reception. This specific technique is known as echo-ranging.

 Additional Information

• Ultrasound refers to sound waves with frequencies above 20,000 Hz, which are beyond the audible range of human hearing.
• Different scientific instruments serve the other functions mentioned:
• Barometer: A scientific instrument primarily used to measure atmospheric pressure to forecast weather changes.
• Ammeter: An electrical instrument used to measure the electric current flowing through a circuit in Amperes.
• Pyrometer: A type of remote-sensing thermometer used to measure exceptionally high temperatures of surfaces, often in industrial furnaces.
• SONAR is also used by marine animals like bats and dolphins (biological sonar) for echolocation to navigate and find prey in dark or murky environments.

The correct answer is 20√10 m/s.

Key Points

• The block is in a state of free fall, which occurs when an object is dropped from a height and moves solely under the influence of gravity.
• The initial velocity (u) is 0 m/s because the object starts from a stationary position at the top of the 200 m building.
• The acceleration due to gravity (g) is constant and given as 10 m/s², acting downwards towards the ground.
• To find the final velocity (v), we utilize the third equation of motion: \( v^2 = u^2 + 2gh \).
• By substituting the known values, the equation becomes: \( v^2 = 0^2 + 2 × 10 × 200 \).
• Simplifying the expression leads to \( v^2 = 4000 \).
• The final velocity (v) is obtained by taking the square root of the result: \( v = \sqrt{4000} = \sqrt{400 × 10} = 20\sqrt{10} \) m/s.

 Additional Information

• Equations of Motion:
• These equations are valid only for objects moving with uniform acceleration.
• First Equation: \( v = u + at \) relates velocity and time.
• Second Equation: \( s = ut + \frac{1}{2}at^2 \) relates displacement and time.
• Conservation of Energy:
• The Potential Energy (PE) at the top (\( mgh \)) is converted into Kinetic Energy (KE) at the ground (\( \frac{1}{2}mv^2 \)).
• Equating PE and KE shows that the velocity is independent of mass, as the variable m cancels out from both sides.
• Free Fall Characteristics:
• In a vacuum, a 20 kg block and a lighter object would hit the ground with the same velocity if dropped from the same height.
• The displacement (s) in vertical motion is simply the height (h) of the fall.

The correct answer is Dialysis removes wastes from blood by diffusion across a semi-permeable membrane..

Key Points

• An artificial kidney is a specialized medical device used to perform hemodialysis, which filters nitrogenous waste products from the blood in patients suffering from renal failure.
• The device contains a series of tubes with a semi-permeable lining (typically made of cellulose) that are submerged in a tank filled with dialysing fluid. Hence, the membrane serves as a selective barrier.
• The dialysing fluid is formulated to have an osmotic pressure identical to blood but is entirely devoid of nitrogenous wastes like urea and uric acid.
• Waste products move from the blood into the dialysing fluid by diffusion, a passive process driven by the concentration gradient across the membrane. Hence, statement 2 is correct.
• In a biological kidney, the renal tubules perform selective reabsorption of glucose, amino acids, and salts; however, an artificial kidney lacks this reabsorption capability. Hence, statement 1 is incorrect.
• The movement of solutes in dialysis does not involve active transport, which requires ATP or cellular energy to move molecules against a gradient. Hence, statement 3 is incorrect.
• While the human Glomerulus utilizes high hydrostatic pressure for ultrafiltration, the fundamental working principle of the dialysis machine is chemical exchange via diffusion. Hence, statement 4 is incorrect.

 Additional Information

• Nitrogenous Waste Products:
• Urea: The primary waste product formed in the liver during the breakdown of proteins.
• Creatinine: A metabolic byproduct of muscle metabolism that must be cleared to prevent toxicity.
• Dialysing Fluid Composition:
• Contains electrolytes such as Sodium, Potassium, and Calcium at physiological levels.
• Includes Bicarbonate to help regulate the pH level of the patient’s blood and neutralize acidity.
• Maintains an isotonic state relative to healthy blood to prevent unwanted fluid shifts.

The correct answer is Formation of ionic bonds.

Key Points

• Carbon is situated in Group 14 of the periodic table with an atomic number of 6 and an electronic configuration of 2, 4. This means it has four electrons in its outermost shell, leading to the property of Tetravalency.
• The term Catenation refers to carbon's unique ability to form strong covalent bonds with other carbon atoms. This allows for the creation of exceptionally long chains, branched structures, and complex rings, which is the foundation of Organic Chemistry.
• Due to its small atomic size, carbon can form multiple bonds, including Single Bonds, Double Bonds, and Triple Bonds. This is possible because the carbon nucleus can effectively hold the shared electrons in pπ-pπ orbital overlaps.
• Carbon does not form Ionic Bonds because losing four electrons to form a C⁴⁺ ion requires an enormous amount of Ionization Energy. Conversely, gaining four electrons to form a C^4- ion would be highly unstable, as a nucleus with six protons cannot easily hold ten electrons.
• The versatility of carbon is strictly due to its ability to share electrons and form stable covalent structures, rather than the transfer of electrons associated with ionic bonding.

 Additional Information

• Tetravalency:
• Enables carbon to bond with four other atoms of carbon or atoms of other monovalent elements like Hydrogen, Chlorine, or Bromine.
• It allows for directional bonding, leading to various geometric shapes like Tetrahedral, Trigonal Planar, and Linear.
• Catenation:
• While elements like Silicon or Sulfur show catenation, the C-C bond energy is much higher, making carbon chains far more stable and less reactive to air and water.
• This property allows for the existence of Isomers, where compounds have the same molecular formula but different structural arrangements.
• Multiple Bond Formation:
• Carbon forms stable multiple bonds with Oxygen, Nitrogen, and Sulfur, which are essential for the functional groups found in biological molecules like proteins and DNA.
• The strength of these bonds is attributed to the Small Atomic Radius of carbon, which ensures a strong nuclear pull on the bonding pair of electrons.

The correct answer is Large, loosely arranged living cells for storage..

Key Points

• Parenchyma is the most fundamental and abundant type of simple permanent tissue, forming the major part of various plant organs like roots, stems, and leaves.
• In a mature dicot stem, the pith (or medulla) occupies the central core and is composed entirely of parenchyma cells that remain living at maturity.
• These cells are typically isodiametric or rounded in shape, possessing thin primary cell walls composed of cellulose and pectin.
• The pith parenchyma is characterized by a loose arrangement with prominent intercellular spaces, which are essential for aeration and the storage of metabolic reserves.
• The primary physiological function of these cells in the pith is the storage of food materials, such as starch, proteins, oils, and water, to support the plant during different growth phases.
• Unlike specialized vascular tissues, parenchyma cells in the pith retain their protoplasm and the potential for cell division, a property known as totipotency.

 Additional Information

• Mechanical and Conducting Tissues:
• Sclerenchyma: These are dead cells at maturity with thick, lignified secondary walls. They provide mechanical strength and rigidity but are not typically found in the central pith of mature herbaceous stems.
• Xylem and Phloem: These are complex tissues specialized for conduction. Xylem consists of vessels and tracheids (dead at maturity) for water transport, whereas the pith is a non-conducting ground tissue.
• Collenchyma: Located usually in the hypodermis (below the epidermis), these living cells have localized pectic thickenings and provide flexible support to growing parts.
• Tissue Distribution: In monocot stems, the ground tissue is not differentiated into a distinct pith and cortex; instead, vascular bundles are scattered throughout the parenchymatous ground tissue.