Why Correct: Carbon dioxide (CO2) accounts for approximately 76% of the total anthropogenic greenhouse effect, making it the dominant contributor among human-caused greenhouse gases.
Distractor Analysis: Hydrogen fluoride is a toxic industrial gas with minimal atmospheric presence and negligible greenhouse impact. Carbon monoxide is primarily an air pollutant that indirectly affects climate by influencing atmospheric chemistry but has weak direct radiative forcing. Sulphur dioxide contributes to aerosol formation and cooling effects rather than greenhouse warming.
Takeaway: Methane (CH4) is the second most significant greenhouse gas at about 16% of total forcing, followed by nitrous oxide (N2O) at 6% and fluorinated gases at 2%.

Why Correct: Water vapor (H2O) is the most abundant greenhouse gas in the atmosphere, accounting for about 60-70% of the greenhouse effect.
Distractor Analysis: CO2 is the second most abundant greenhouse gas, primarily from human activities. CH4 (methane) is present in much smaller concentrations but has a higher global warming potential. CO (carbon monoxide) is not a greenhouse gas; it does not absorb infrared radiation significantly.
Takeaway: Water vapor dominates the natural greenhouse effect, while CO2 is the key anthropogenic greenhouse gas targeted in climate policies.

Why Correct: Sulfur dioxide (SO2) does not absorb infrared radiation in the Earth's thermal infrared window, thus it does not contribute to the greenhouse effect. Greenhouse gases like CH4, N2O, and H2O have vibrational modes that trap outgoing longwave radiation.
Distractor Analysis: CH4 (methane) absorbs at 3.3 and 7.6 micrometers, making it a potent greenhouse gas. N2O (nitrous oxide) absorbs at 4.5 and 7.8 micrometers, also a greenhouse gas. H2O (water vapor) is the most abundant greenhouse gas, with broad absorption bands. SO2 primarily affects atmospheric chemistry and aerosol formation, not longwave radiation absorption.
Takeaway: Common greenhouse gases: CO2, CH4, N2O, H2O, O3, CFCs. SO2 is not a greenhouse gas; it is a precursor to acid rain and particulate matter.

Why Correct: Methane (CH4) is a potent greenhouse gas that traps infrared radiation in Earth's atmosphere, contributing to global warming. Its global warming potential is about 25 times that of CO2 over 100 years.
Distractor Analysis: Nitrogen (N2) makes up 78% of the atmosphere but is not a greenhouse gas because it does not absorb infrared radiation. Chlorine (Cl2) is a reactive gas used in disinfection, not a greenhouse gas; it is involved in ozone depletion instead. Acetylene (C2H2) is a hydrocarbon used as a fuel, but its atmospheric concentration is negligible, and it is not classified as a major greenhouse gas.
Takeaway: The four primary greenhouse gases are CO2, CH4, N2O, and fluorinated gases. Methane is released from agriculture (livestock, rice paddies), landfills, and fossil fuel extraction.

Why Correct: Carbon dioxide accounts for approximately 14% of the total greenhouse effect, making it the second most important greenhouse gas after water vapor.
Distractor Analysis: 49% roughly corresponds to the combined effect of clouds and water vapor. 18% is the contribution from other greenhouse gases like methane and nitrous oxide. 13% is close but the widely cited figure for CO2 is 14%.
Takeaway: Remember the greenhouse gas contribution pie: Water vapor ~60%, CO2 ~14%, clouds ~25%, others ~1%. For competitive exams, the 14% figure for CO2 is a standard fact to recall.

Why Correct: The G-8 (Group of Eight) at the 2007 Heiligendamm summit committed to halving global greenhouse gas emissions by 2050 as part of the post-Kyoto framework.
Distractor Analysis: United Nations is the overarching body but not the entity that set the 50% target; UNDP focuses on development programs, not emission reduction goals; SAARC is a regional South Asian cooperation bloc that has not issued such a global target.
Takeaway: The G-8's 50% reduction pledge was a precursor to the Copenhagen Accord; examinees should associate major emission targets with the G-8/G-20 rather than the UN general bodies.

Why Correct: India announced its net-zero carbon emission target of 2070 at the COP26 summit in Glasgow (2021), as part of its Panchamrit commitments. This target aligns with India's long-term low-carbon development strategy.
Distractor Analysis: 2050 is the net-zero target year adopted by many developed countries and the EU, but not by India. 2060 is China's announced net-zero target year. 2100 is a generic far-future year sometimes cited in climate scenarios, but not India's official commitment.
Takeaway: India's Panchamrit commitments at COP26 include: 500 GW non-fossil fuel capacity by 2030, 50% energy from renewables by 2030, reduction of 1 billion tonnes of projected carbon emissions, reduction of emissions intensity by 45% by 2030, and net-zero by 2070.