Science — Natural Resources — Practice

Question 1

By volume, dry air contains approximately what percentage of oxygen?
(a) 78%  (b) 21%  (c) 1%  (d) 99%

Accepted Answer

Dry air is roughly 78% nitrogen and 21% oxygen by volume, with about 1% made up of argon, carbon dioxide, water vapour, and dust.

Answer: (b) 21%. Trap (a) 78% swaps oxygen's share for nitrogen's, the single most common confusion with this fact. Trap (c) 1% wrongly assigns oxygen the share actually held by the 'other gases' category. Trap (d) 99% wrongly treats oxygen as nearly the entirety of air, ignoring nitrogen's much larger share.

Question 2

Acid rain, which has damaged monuments such as the Taj Mahal, results chiefly from which pollutants dissolving in rainwater?
(a) Carbon monoxide and methane  (b) Sulphur dioxide and oxides of nitrogen  (c) Chlorofluorocarbons  (d) Suspended particulate matter

Accepted Answer

Sulphur dioxide and nitrogen oxides, released mainly by burning fossil fuels, dissolve in atmospheric moisture to form sulphuric and nitric acid, which then fall as acid rain.

Answer: (b) Sulphur dioxide and oxides of nitrogen. Trap (a) confuses acid rain's cause with carbon monoxide, which is a poisoning hazard from incomplete combustion, not an acid-rain precursor. Trap (c) misattributes acid rain to CFCs, which are instead responsible for ozone-layer depletion, a separate mechanism entirely. Trap (d) confuses SPM's respiratory-harm effect with the distinct chemical process that produces acid rain.

Question 3

The process by which plants release water vapour into the atmosphere, contributing to the water cycle alongside evaporation, is called:
(a) Condensation  (b) Precipitation  (c) Transpiration  (d) Infiltration

Accepted Answer

Transpiration is the release of water vapour from plant leaves into the atmosphere, working alongside evaporation from open water bodies to feed the water cycle's condensation stage.

Answer: (c) Transpiration. Trap (a) Condensation is the later stage where rising water vapour cools into clouds, not the plant-release stage itself. Trap (b) Precipitation is water falling back to Earth as rain or snow, the opposite direction of the process described. Trap (d) Infiltration describes water soaking into the ground after precipitation, an unrelated stage of the cycle.

Question 4

Which of the following is NOT a commonly cited cause of falling groundwater tables in parts of India?
(a) Over-extraction through tube wells for irrigation
(b) Reduced recharge due to urban concretisation
(c) Increased forest cover slowing surface runoff
(d) Increasingly erratic monsoon rainfall

Accepted Answer

Increased forest cover actually aids groundwater recharge by slowing runoff and letting more water infiltrate the soil — it is a conservation measure, not a cause of depletion, making it the odd one out among the four options.

Answer: (c) Increased forest cover slowing surface runoff. Options (a), (b), and (d) are all genuine, commonly cited drivers of groundwater depletion — over-extraction for irrigation, reduced recharge from concretised urban surfaces, and erratic rainfall reducing natural replenishment.

Question 5

The Chipko movement, in which villagers (prominently women) embraced trees to prevent them from being felled, is NCERT's standard example of:
(a) Government-led afforestation policy
(b) A grassroots forest conservation movement
(c) Scientific soil-testing methodology
(d) A water-conservation technique

Accepted Answer

The Chipko movement of the 1970s, centred in the Himalayan foothills, is cited as a community-driven, grassroots response to protect forest cover from felling — not a government policy, a soil method, or a water-conservation practice.

Answer: (b) A grassroots forest conservation movement. Trap (a) wrongly attributes the movement's origin to government policy, when it was in fact a community-initiated response. Trap (c) and trap (d) both misplace the movement into unrelated categories of this chapter — soil testing and water conservation are distinct themes covered separately.

Question 6

Which layer of the soil profile is dark, humus-rich, and supports the most root growth and biological activity?
(a) Horizon B  (b) Horizon C  (c) Horizon A  (d) Bedrock

Accepted Answer

Horizon A, the topsoil, is dark and humus-rich from decomposed organic matter, and is where most root growth, biological activity, and agricultural fertility are concentrated.

Answer: (c) Horizon A. Trap (a) Horizon B is the subsoil beneath topsoil — lighter in colour, with less humus and more accumulated minerals, not the most fertile layer. Trap (b) Horizon C consists of partially weathered parent-rock fragments, well below the biologically active zone. Trap (d) Bedrock is solid, unweathered rock at the very base of the profile, with no soil characteristics at all.

Question 7

Cutting a hillside into a series of flat, step-like fields to slow water runoff and reduce soil erosion on slopes is known as:
(a) Contour ploughing  (b) Strip cropping  (c) Terrace farming  (d) Crop rotation

Accepted Answer

Terrace farming cuts a sloped hillside into a series of flat, step-like platforms, directly slowing the speed of water runoff and reducing soil loss on steep terrain.

Answer: (c) Terrace farming. Trap (a) Contour ploughing follows a slope's natural contour lines while ploughing, a related but distinct technique that doesn't involve reshaping the land into steps. Trap (b) Strip cropping alternates different crops in parallel strips, a technique aimed at limiting erosion spread rather than reshaping slope geometry. Trap (d) Crop rotation varies which crop is grown each season to preserve soil fertility, unrelated to slope-erosion control specifically.

Question 8

A student argues that coal and petroleum should be called 'renewable' because the same geological processes that formed them originally are technically still occurring today. What is the most accurate response to this argument, consistent with how NCERT classifies these resources?
(a) The student is correct — they should be reclassified as renewable
(b) They remain non-renewable, because formation takes millions of years, far exceeding the rate of human consumption
(c) They are non-renewable only because they cause pollution when burned
(d) They are non-renewable because they are found only in a few specific countries

Accepted Answer

Renewability is a practical classification about whether a resource replenishes within a timescale relevant to human use — coal and petroleum formation, occurring over millions of years, fails that test by many orders of magnitude, regardless of whether the underlying geological process continues somewhere today.

Answer: (b). Trap (a) accepts the student's flawed reasoning, missing the distinction between geological continuity and human-relevant timescale. Trap (c) misattributes the classification to pollution, which is a separate concern from renewability entirely — a resource could pollute heavily and still be renewable, or be clean-burning and still be non-renewable. Trap (d) misattributes the classification to geographic distribution, which has no bearing on whether a resource replenishes fast enough to be renewable.

Question 9

Why must water never be used to extinguish an electrical fire?
(a) Water evaporates too quickly to have any cooling effect
(b) Water conducts electricity, risking electric shock to whoever uses it
(c) Water increases the fire's ignition temperature
(d) Water reacts chemically with electrical wiring to produce more heat

Accepted Answer

Water conducts electric current, so directing it at a live electrical fire creates a serious risk of electric shock to the person attempting to extinguish it — carbon dioxide, which doesn't conduct electricity and smothers the fire by cutting off oxygen, is the correct choice instead.

Answer: (b) Water conducts electricity, risking electric shock. Trap (a) is factually wrong — water's cooling effect is exactly why it works well on ordinary wood or paper fires; the issue with electrical fires is conductivity, not evaporation speed. Trap (c) reverses the actual mechanism — water lowers a fuel's temperature below its ignition point, it doesn't raise it. Trap (d) invents a chemical reaction between water and wiring that isn't the actual danger; the real risk is water's electrical conductivity providing a shock path.

Practice — Science — Natural Resources

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