Q.Which of the following would most likely help to slow down the greenhouse effect.
Concept understanding — Greenhouse Effect and Global Warming
Greenhouse Effect and Global Warming
The greenhouse effect is the natural warming of the Earth caused by certain atmospheric gases. Sunlight reaches the Earth's surface, which absorbs it and re-emits heat as infrared (long-wave) radiation. Greenhouse gases — chiefly carbon dioxide (CO₂) and methane (CH₄), along with water vapour, nitrous oxide (N₂O) and chlorofluorocarbons (CFCs) — absorb and trap this outgoing infrared radiation, preventing its escape to space and reheating the atmosphere.
Without this effect the Earth would be too cold for life; however, rising anthropogenic emissions intensify it, causing global warming — an increase in average global temperature.
Relative contribution to global warming (approximate): CO₂ ≈ 60%, methane ≈ 20%, CFCs ≈ 14%, and N₂O ≈ 6% (values vary between sources). Methane, though present in smaller amounts, is a far more potent greenhouse gas per molecule than CO₂.
Consequences include melting of polar ice, rising sea levels, and shifts in rainfall and agriculture. Mitigation involves cutting fossil-fuel use, reforestation and reducing emissions of these gases.
This concept covers CET questions on the mechanism of the greenhouse effect, identification of greenhouse gases, and their relative contribution to global warming.
The greenhouse effect and global warming are covered in the environmental-issues chapter of NCERT Class 12 Biology, and "greenhouse gases and their relative contribution to global warming" is a frequently searched revision topic. This is a dependable source of important questions in NEET and CET biology exams because of the precise percentage contributions attributed to gases like methane and carbon dioxide.
Capturing methane from landfills instead of letting it vent into the air removes a potent greenhouse gas at its source, so it is the option that helps slow the greenhouse effect.
(c) Redesigning landfill dumps to allow methane to be collected.
Step 1. Evaluate each option against what actually adds to or removes greenhouse gases. Converting tropical forest to grazing land (a) destroys a carbon sink and adds cattle-linked methane — it worsens the greenhouse effect, not slows it.
Step 2. Burying excess paper packaging 'to ashes' (b) implies incineration, which releases stored carbon as CO2 rather than sequestering it, so it also adds to greenhouse gas load.
Step 3. Landfills are a major uncontrolled source of methane (CH4), a greenhouse gas roughly 20 times more effective than CO2 at trapping heat. Redesigning landfill dumps so this methane is collected (c) — rather than escaping to the atmosphere — directly removes a potent greenhouse gas from circulation, and the collected gas can even be burned for electricity instead of vented raw.
Step 4. Promoting private over public transport (d) increases per-passenger fuel combustion and CO2 emissions, worsening rather than easing the greenhouse effect.
Only option (c) — capturing landfill methane — actively removes a greenhouse gas rather than adding one, making it the correct choice.
Test each option for whether it adds or removes a greenhouse gas; only landfill-methane capture removes one.
- Picking (a) or (d) by only noticing 'natural'-sounding land use without checking the emissions it actually causes.
- Assuming incineration (b) is equivalent to safe disposal rather than a CO2-releasing process.
Showing the 12 most recent of 17 on this concept.
- CBSE 2025Set ANNUAL1 markMCQQ.Which one of the following are greenhouse gases?(a) CO2, CFC, CH4, N2O(b) CO2, NO2, NH3, N2O(c) CH4, N2, NH3, CO2(d) CFC, CO2, N2O, NH3
›Reveal solutionSolution
The major greenhouse gases are carbon dioxide, CFCs, methane, and nitrous oxide.
Greenhouse gases trap outgoing long-wave (infrared) radiation from the Earth's surface, warming the atmosphere. The principal greenhouse gases are CO2 (carbon dioxide), CFCs (chlorofluorocarbons), CH4 (methane), and N2O (nitrous oxide), along with water vapour. Gases like N2, NH3, and NO2 (in the forms listed in the distractor options) are not classified among the primary greenhouse gases in this standard list.
✓Final answerCO2, CFC, CH4, N2O — the standard set of major greenhouse gases.
- CBSE 2024Set E1 markMCQQ.Which of the following is not the reason for global warming?(a) Use of fossil fuels(b) Deforestation(c) Population explosion(d) Improvement in the efficiency of energy use
›Reveal solutionSolution
Fossil-fuel use, deforestation and population explosion all worsen global warming; improving energy-use efficiency is a mitigation measure, not a cause.
Global warming is driven by rising greenhouse gases. Burning fossil fuels releases carbon dioxide, deforestation removes the carbon sinks that absorb it, and population explosion increases overall consumption and emissions — all of these intensify global warming. Improving the efficiency of energy use, on the other hand, lowers fuel consumption and emissions and is one of the recommended steps to REDUCE global warming, so it is not a cause.
✓Final answer(d) Improvement in the efficiency of energy use.
- CBSE 2024Set ANNUAL1 markMCQQ.One green house gas contributes 20% of total global warming and another contributes 60%. These are respectively identified as :(a) CH4 and CO2(b) N2O and CO2(c) CH4 and CFCs(d) CFCs and N2O
›Reveal solutionSolution
The gas contributing about 20% of global warming is methane (CH4) and the gas contributing about 60% is carbon dioxide (CO2), in that order -- option (a).
Working
Several gases contribute to the enhanced greenhouse effect and global warming, each in different proportions based on its atmospheric concentration and heat-trapping ability. Carbon dioxide (CO2), released mainly from fossil fuel combustion and deforestation, is by far the largest contributor by total effect, conventionally cited at around 60% of the overall greenhouse contribution because of its sheer volume in the atmosphere. Methane (CH4), released from sources like paddy fields, livestock, and landfills, is a much more potent heat-trapping gas per molecule than CO2, but is present in far smaller quantities, giving it a smaller overall share, conventionally cited around 20%. Matching the question's "one gas 20%... another 60%" to this order gives CH4 (20%) and CO2 (60%) respectively. The other options pair in gases like N2O or CFCs, which are real greenhouse gases but do not match these specific commonly-cited percentage contributions.
✓Final answerThe correct option is (a): CH4 and CO2
- CBSE 2023Set ANNUAL1 markMCQQ.Main example of greenhouse gas is -(a) Nitrogen(b) Carbon monoxide(c) Methane(d) Oxygen
›Reveal solutionSolution
Greenhouse gases trap infrared (heat) radiation reflected from the Earth's surface, causing global warming; methane is a well-known greenhouse gas, while nitrogen and oxygen are not.
Greenhouse gases absorb and re-radiate infrared radiation, warming the lower atmosphere (the greenhouse effect). The principal greenhouse gases are carbon dioxide, methane, nitrous oxide, chlorofluorocarbons (CFCs), water vapour and ozone.
Nitrogen and oxygen make up the bulk of the atmosphere but are transparent to infrared radiation and are not counted as greenhouse gases; carbon monoxide is a toxic air pollutant but is not classified among the principal greenhouse gases in the NCERT list.
✓Final answer(c) Methane - a major greenhouse gas.
- CBSE 2023Set ANNUAL1 markMCQQ.Which of the following is not green house gas ?(a) CO_2(b) CH_4(c) CFCS(d) O_2
›Reveal solutionSolution
O2 is not a greenhouse gas.
Greenhouse gases trap outgoing infrared (heat) radiation and warm the atmosphere. Carbon dioxide (CO2), methane (CH4) and chlorofluorocarbons (CFCs) are all effective greenhouse gases. Molecular oxygen (O2), being a homonuclear diatomic molecule with no change in dipole moment on vibration, does not absorb IR radiation and therefore does not contribute to the greenhouse effect.
The greenhouse effect is a key topic in the NCERT Class 11 Chemistry chapter Environmental Chemistry.
✓Final answer(d) O2.
- CBSE 2022Set ANNUAL1 markMCQQ.One greenhouse gas contributes 14% of total global warming and another contributes 60%. These are respectively identified as :(a) CH4 and CO2(b) N2O and CO2(c) CH4 and CFC(d) CFC and CO2
›Reveal solutionSolution
Of the two gases named, the 14% contributor is CFC and the 60% contributor is CO2.
The overall greenhouse effect is driven by several gases that absorb and re-radiate infrared radiation, but they do not all contribute equally. Carbon dioxide, released mainly by fossil-fuel combustion, deforestation and industrial processes, is both the most abundant and (cumulatively) the single largest contributor to global warming among these gases, commonly cited at about 60% of the total effect. Chlorofluorocarbons, entirely artificial compounds once widely used as refrigerants, propellants and solvents, are present in the atmosphere in far smaller quantities than CO2, but each CFC molecule has a very high global-warming potential (it absorbs infrared radiation far more strongly, molecule for molecule, than CO2), so CFCs are typically credited with about 14% of total global warming despite their low concentration -- this is also why the Montreal Protocol specifically targeted CFCs for phase-out. Methane (from cattle, paddy fields, landfills and fossil-fuel extraction) and nitrous oxide (from fertiliser use and combustion) contribute smaller shares, typically cited at around 20% and 6% respectively in standard textbook breakdowns, so the specific 14% and 60% figures in this question point to CFC and CO2, not to CH4 or N2O.
✓Final answerThe gas contributing 14% is CFC and the gas contributing 60% is CO2.
- CBSE 2022Set ANNUAL1 markMCQQ.Which of the following emits methane?(a) paddy field(b) animals(c) termites(d) all of these
›Reveal solutionSolution
Paddy fields, animals and termites all emit methane, so the answer is (D).
Methane (CH4) is a potent greenhouse gas produced by anaerobic decomposition (methanogenesis). Major biological sources include: flooded paddy (rice) fields, where waterlogged soils are anaerobic; the digestive tracts of ruminant animals like cattle, which harbour methanogenic archaea; and termites, whose gut microbes generate methane. Since all three are genuine sources, the answer is 'all of these'.
✓Final answer(D) all of these.
- CBSE 2021Set D1 markMCQQ.Which of the following is not a greenhouse gas ?(a) Methane(b) Chlorofluorocarbon(c) CO2(d) Nitrogen
›Reveal solutionSolution
Nitrogen (N2) does not trap infrared radiation and is not a greenhouse gas, so the answer is (D).
Greenhouse gases absorb and re-radiate infrared (heat) radiation, warming the Earth's surface. The major greenhouse gases are carbon dioxide (CO2), methane (CH4), chlorofluorocarbons (CFCs), nitrous oxide and water vapour.
Molecular nitrogen (N2), although it makes up about 78% of the atmosphere, is a symmetrical diatomic molecule that does not absorb infrared radiation and therefore is not a greenhouse gas. Hence, out of the given options, nitrogen is not a greenhouse gas.
✓Final answer(D) Nitrogen.
- CBSE 2021Set OC_ZOOLOGY1 markQ.Name the gas that contributes mainly to global warming.
›Reveal solutionSolution
Carbon dioxide (CO₂), released chiefly by burning fossil fuels and deforestation, is the greenhouse gas that contributes the most to global warming.
The greenhouse effect and global warming
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Certain atmospheric gases (called greenhouse gases) allow sunlight to pass through and reach the Earth's surface, but trap the outgoing infrared (heat) radiation, warming the atmosphere — this natural process is the greenhouse effect.
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Human activities have sharply increased the concentration of these gases, intensifying the greenhouse effect and causing global warming.
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The main greenhouse gases are carbon dioxide, methane, nitrous oxide, water vapour, and chlorofluorocarbons (CFCs).
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Of these, CO₂ — produced mainly by burning coal and petroleum for energy and transport, and by large-scale deforestation which removes a major carbon sink — is emitted in by far the largest quantity, and so is regarded as the single biggest contributor to global warming.
✓Final answerCarbon dioxide is the gas that contributes the most to global warming.
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- CBSE 2019Set BOTANY1 markMCQQ.Fill in the blank selecting the appropriate term given under the bit: The most common and abundant greenhouse gas is ____.(a) methane(b) CFC(c) carbon dioxide(d) nitrous oxide
›Reveal solutionSolution
Carbon dioxide, released mainly by burning of fossil fuels and deforestation, is present in the atmosphere in far greater quantity than the other greenhouse gases and is responsible for roughly half of the observed global warming.
Several gases in the atmosphere trap outgoing infrared radiation and produce the greenhouse effect, including carbon dioxide, methane, chlorofluorocarbons (CFCs) and nitrous oxide.
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Carbon dioxide (CO2) is released continuously through the combustion of fossil fuels (coal, petroleum), deforestation and various industrial processes. Because its atmospheric concentration is far higher than that of the other greenhouse gases, it is considered the most common/abundant greenhouse gas and the single biggest contributor to the enhanced greenhouse effect and global warming.
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Methane, CFCs and nitrous oxide, though individually more potent per molecule at trapping heat, occur in much smaller concentrations, so their overall contribution is smaller than that of CO2.
✓Final answer(c) carbon dioxide.
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- CBSE 2019Set ANNUAL1 markMCQQ.Which among the following is not a greenhouse gas ?(a) N2O(b) Methane(c) Carbon dioxide(d) Ozone
›Reveal solutionSolution
Of the four options, carbon dioxide, methane and nitrous oxide (N2O) are the greenhouse gases that trap infra-red radiation and cause global warming; ozone is treated separately in the syllabus, as the layer that shields the Earth from UV-B (its depletion, not the greenhouse effect, is the issue associated with it).
Greenhouse gases are those atmospheric gases that absorb and re-radiate infra-red (heat) radiation reflected from the Earth's surface, trapping heat in the atmosphere and warming the planet (the 'greenhouse effect'). The gases most responsible for the recent rise in global warming are carbon dioxide (CO2 — from fossil-fuel burning and deforestation), methane (CH4 — from paddy fields, cattle, landfills), nitrous oxide (N2O — from fertiliser use, combustion) and chlorofluorocarbons (CFCs).
Ozone (O3), by contrast, is dealt with under a separate environmental issue in this chapter: the depletion of the stratospheric ozone layer by CFCs, which lets in more harmful ultraviolet (UV-B) radiation. So among the given options, ozone is the one that is not counted among the standard greenhouse gases causing global warming.
✓Final answer(d) Ozone — CO2, methane and N2O are greenhouse gases that cause global warming; ozone's environmental role covered here is its depletion (letting in UV-B), not the greenhouse effect.
- CBSE 2018Set ANNUAL1 markQ.Write name of any two green house gases.
›Reveal solutionSolution
Greenhouse gases are atmospheric gases that trap heat radiated from the earth's surface, causing global warming; common examples include carbon dioxide and methane.
Greenhouse gases absorb and re-radiate infrared (heat) radiation reflected from the earth's surface, warming the lower atmosphere - the greenhouse effect. The major greenhouse gases are carbon dioxide (CO2), released mainly by burning of fossil fuels and deforestation, and methane (CH4), released from paddy fields, ruminant digestion (cattle), and landfills. (Other accepted examples include nitrous oxide, chlorofluorocarbons (CFCs), and water vapour - any two of these gases is a correct answer.)
✓Final answerTwo greenhouse gases: carbon dioxide (CO2) and methane (CH4).
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