General Science MCQ Practice

Correct answer: C

• Why it’s correct: Ocean thermal energy relies on the temperature difference between warm surface water and cold deep water to drive work (OTEC).
• Key concept: Thermodynamic gradient enables heat transfer to power a cycle (often a Rankine-like cycle) using two temperature reservoirs.
• Simple formula (conceptual): Q = m·c·ΔT for heat transfer between layers; larger ΔT yields more energy.
• Exam tip: Remember: not tides, pressure, or waves—it's the thermal gradient with depth.
• Why others are incorrect: A: tides are gravitational; B: pressure differences are not the energy source for OTEC; D: waves store energy, not the basic source for OTEC.

Correct option: B

• Why correct: Sodium bicarbonate (NaHCO3) decomposes on heating to release CO2, which cools and smothers the fire in dry chemical extinguishers.
• Key concept: Fire extinguishing by blocking heat and reducing fuel/oxygen via gas release.
• Formula note: NaHCO3 → NaNaCO3 (or Na2CO3) + CO2 + H2O under heating.
• Why others are incorrect: - A) Sodium carbonate is less effective and lacks rapid CO2 release. - C) Sodium nitrate is an oxidizer, fuels fire. - D) Sodium sulphate is inert in extinguishing action.
• Exam tip: Remember bicarbonate for small portable extinguishers (dry chemical type).

Correct option: C (Biome)

• Why: A biome is a major, large-scale ecological unit characterized by climate and vegetation patterns that occur across large geographic areas, making it the largest among the options.
• Key concept: Scale in ecology: organism → population → ecosystem → biome.
• Other options:
  • Organism: a single living thing.
  • Population: individuals of one species in an area.
  • Ecosystem: living organisms plus their physical environment in a region.
• Exam tip: Remember the hierarchy: organism < population < ecosystem < biome (largest).

• Correct answer: D — A fuse wire should heat up and melt when overcurrent occurs.
• Key concept: Power dissipated as heat is P = I^2R. A fuse needs high resistance to generate more heat, and a low melting point so it melts quickly.
• Why D is correct: High resistive material converts more electrical energy into heat; low melting point allows rapid melting.
• Incorrect options: A would not melt easily due to high melting point; B and C have too low heat generation or too high melting point for reliable fusing.
• Exam tip: Remember: fuse = high resistance + low melting point for quick protection.

Sustainable development is the growth and development that meets present needs without compromising future generations’ ability to meet theirs. Key concept: balancing economic, social, and environmental needs (three pillars). Why correct: It explicitly aims to conserve resources while allowing ongoing human progress. Formula/logic (brief): Intergenerational equity + precautionary approach + resource efficiency = sustainable outcome. Exam tip: Remember the phrase “meets present needs without compromising the future.” Other options:

• A. Green economy — focuses on environmental sustainability but not explicitly intergenerational equity.
• B. Holistic development — broad concept, not specific to resource conservation.
• D. Subsistence agriculture — relates to low-input farming, not sustainable development.

Explanation:

• Correct answer: C — Newton’s third law: every action has an equal and opposite reaction.
• In a rocket, fast-moving exhaust gas is expelled backward, creating a forward thrust on the rocket.
• This thrust arises from action-reaction pairs and is how momentum is exchanged (conservation of momentum).
• Why not A or B? Newton’s first law is about objects at rest or in uniform motion unless acted on; not the propulsion mechanism. Second law relates force, mass, and acceleration of the rocket as a whole, but thrust originates from the third-law pair.

Exam tip: Remember rockets move due to action-reaction, not just due to overall force on the rocket.

Answer: A. Agriculture

• Key concept: Green Revolution refers to the rapid adoption of high-yielding crop varieties, modern inputs (irrigation, fertilizers, pesticides) and improved farming practices in agriculture.
• Why correct: It mainly transformed crop production and food crops, boosting yields in farming systems.
• Why others are incorrect: Sericulture (silk farming), fishery (aquaculture) and beekeeping are different sectors, not the core focus of the Green Revolution.
• Formula/numerical note: Yield gain ≈ (yield with inputs) − (yield without inputs); increases are per hectare.
• Exam tip: Remember: Green Revolution = high-yield varieties + modern inputs in agriculture.

Correct option: B
Answer: Nitrous oxide.

• Reason: Nitrous oxide (N2O) is a commonly used anaesthetic gas for inhalation anesthesia in dentistry and surgery.
• Key concept: Anaesthetic gases reduce neuronal activity to induce loss of sensation and consciousness.
• Why others are incorrect:
  • Nitrogen dioxide (A)
  —toxic and irritant, not an anaesthetic.
  • Nitric oxide (C)
  —a signaling gas with various roles, not a routine anaesthetic.
  • Nitrogen (D)
  —inert, non-anaesthetic gas.

Exam tip: Memorize N2O as “laughing gas” commonly used as an anaesthetic.

• Answer: A is not correct.
• Why: Color-revolution names map to specific sectors. Green = food grains, White = milk, Yellow = oilseeds, Blue = fisheries, Pink = fruits/vegetables, Purple/others vary. Silver Revolution is commonly linked to poultry eggs, not pulses.
• Concept: National “revolutions” denote rapid growth in a sector; key idea is color-coded agricultural milestones.
• Tip: If unsure, match color with its most famous product from exam memory aids.
• Why others are correct (brief): B, C, D align with established mappings (milk, food grains, oilseeds) in standard references.

The process is bioremediation (Option B). Key concept: using living organisms (bacteria, plants) to detoxify or remove pollutants from soil or water. Why correct: Microorganisms metabolize contaminants, converting them into less harmful substances, thus cleaning the environment. Notes: - Biotechnology (A) is wider and includes tools/techniques, not limited to cleaning. - Biodegradation (C) is the breakdown of substances by organisms, but bioremediation focuses on removing pollutants. - Biomagnification (D) is the increasing concentration of a substance up the food chain, not remediation. Exam tip: Look for "using living organisms to remove pollutants"—that defines bioremediation.