Greenhouse effect and global warming

Correct answer: A. It absorbs some outgoing heat and contributes to the greenhouse effect

Explanation: The correct answer is A: carbon dioxide is a greenhouse gas. Earth’s surface emits energy as infrared radiation, and carbon dioxide absorbs some of this outgoing radiation and re-emits energy in different directions, including back toward the surface. This natural greenhouse effect helps keep Earth warm; increasing carbon dioxide in the atmosphere adds to warming. Nitrogen, not carbon dioxide, is the most abundant gas in the atmosphere.

Correct answer: A. It absorbs some infrared radiation emitted by Earth and helps retain heat in the atmosphere

Explanation: A is correct. Earth emits energy as infrared radiation, and carbon dioxide absorbs some of this outgoing radiation and re-emits it in different directions. This helps retain heat in the atmosphere. Nitrogen, not carbon dioxide, is the most abundant gas in the atmosphere.

Correct answer: A. Greenhouse gas — हरितगृह गैस

Explanation: The correct answer is A, a greenhouse gas. Methane absorbs some of the infrared radiation emitted by Earth and contributes to the greenhouse effect. It is a trace gas, not one of the main permanent gases such as nitrogen or oxygen; a condensation nucleus is a particle, not a gas.

Correct answer: A. Carbon dioxide

Explanation: Carbon dioxide (CO₂) contributes to the greenhouse effect, so A is correct. It absorbs some outgoing infrared radiation and re-emits energy, helping warm the lower atmosphere. Argon and nitrogen do not absorb this radiation significantly, and dust particles are not a gas.

Correct answer: A. Both contribute to the greenhouse effect

Explanation: The correct answer is A. Carbon dioxide and water vapour absorb some of the outgoing infrared radiation emitted by Earth’s surface and contribute to the greenhouse effect. Neither is chemically inert, neither is the most abundant atmospheric gas, and neither is a dust particle.

Correct answer: A. Greenhouse effect

Explanation: Correct answer: A. Water vapour and carbon dioxide are greenhouse gases. Earth’s surface emits infrared energy, and these gases absorb and re-emit some of it, helping retain heat in the atmosphere. This natural greenhouse effect helps keep Earth warm enough for life.

Correct answer: A. Both absorb some outgoing infrared radiation and contribute to the greenhouse effect.

Explanation: Answer: A. Earth’s surface emits infrared radiation, and both carbon dioxide and water vapour absorb some of it. This contributes to the greenhouse effect. They are not inert gases or dust particles, and neither is the main gas used in ordinary aerobic respiration.

Correct answer: A. Both contribute to the greenhouse effect

Explanation: The correct answer is A. Both carbon dioxide and water vapour absorb and emit infrared radiation, so both contribute to Earth's natural greenhouse effect. Their behaviour differs: atmospheric water vapour changes rapidly with the water cycle and temperature, while carbon dioxide persists longer in the atmosphere.

Correct answer: B. Atmosphere trapping some heat

Explanation: The greenhouse effect is the natural process in which gases such as water vapour, carbon dioxide, methane, and nitrous oxide absorb and re-radiate part of Earth's outgoing longwave radiation. This retention of heat warms the lower atmosphere and surface. The natural effect is essential for a habitable average temperature.

Correct answer: C. Carbon dioxide

Explanation: Carbon dioxide is a major greenhouse gas because its molecules absorb and re-emit part of Earth's outgoing infrared radiation. Its concentration has increased substantially because of fossil-fuel combustion, cement production, and land-use change. Nitrogen, oxygen, and helium are not significant greenhouse gases under ordinary atmospheric conditions.

Correct answer: B. It retains some heat in the atmosphere, keeping Earth habitable

Explanation: The natural greenhouse effect keeps part of Earth's outgoing longwave heat within the lower atmosphere. Water vapour, carbon dioxide, methane, and other gases absorb and re-radiate this energy, preventing the planet from becoming too cold. Without this natural warming, Earth's average surface temperature would be far less suitable for liquid water and life.

Correct answer: B. Enhanced greenhouse effect

Explanation: When activities such as burning coal, oil, and gas, deforestation, industry, and intensive agriculture increase greenhouse-gas concentrations, the atmosphere absorbs more outgoing heat than it would under natural conditions. This human-driven strengthening is called the enhanced greenhouse effect and is a major cause of current global warming.

Correct answer: A. Carbon dioxide

Explanation: Combustion of coal, petroleum, and natural gas oxidises carbon and releases carbon dioxide into the atmosphere. Large-scale energy use, transport, electricity generation, and industry therefore raise atmospheric CO2 concentrations. Neon, argon, and hydrogen are not the principal greenhouse-gas emissions produced by ordinary fossil-fuel combustion.

Correct answer: B. It reduces the absorption of carbon dioxide

Explanation: Forests act as carbon sinks: growing vegetation removes carbon dioxide from the air through photosynthesis and stores carbon in biomass and soils. Deforestation reduces this uptake and often releases stored carbon through burning or decomposition. Consequently, more CO2 remains in the atmosphere, strengthening the greenhouse effect and contributing to global warming.

Correct answer: A. Because it can absorb heat radiation

Explanation: Water vapour absorbs and re-emits portions of the infrared radiation emitted by Earth's surface, so it contributes strongly to natural atmospheric heat retention. Its amount is controlled largely by temperature through evaporation and condensation, making it an important feedback in climate change. It does not form rocks, stop earthquakes, or alter Earth's orbit.

Correct answer: A. Rise in average temperature

Explanation: A higher concentration of greenhouse gases increases the absorption of outgoing longwave radiation and disturbs Earth's energy balance. Over time, this positive radiative forcing can raise global and regional average temperatures, although the exact response varies by place and season. It does not eliminate gravity, shorten the day suddenly, or make continents disappear.

Correct answer: A. Melting of glaciers and ice sheets

Explanation: Global warming can cause glaciers and land-based ice sheets to lose mass. Meltwater then flows into the oceans, adding water and raising sea level. Warming also causes seawater to expand thermally, which is another important contributor. In contrast, desert sand, stars, and Earth's rotation do not explain this climate-related rise in sea level.

Correct answer: A. Because naturally it keeps Earth warm enough for life

Explanation: The natural greenhouse effect is essential because it retains enough outgoing heat to keep Earth's surface warmer than it would otherwise be. This supports liquid water and ecosystems. The problem is not the natural effect itself but its enhancement by human emissions, which adds excessive radiative forcing and contributes to long-term global warming and climate disruption.

Correct answer: A. Energy efficiency and clean energy use

Explanation: Improving energy efficiency reduces the amount of fuel needed for the same service, while renewable and other low-carbon energy sources reduce greenhouse-gas emissions from electricity, transport, and industry. These are mitigation measures. Burning more coal, wasting fuel, and deforestation increase emissions or remove carbon sinks, so they intensify rather than reduce global warming.

Correct answer: A. Nitrous oxide

Explanation: Nitrous oxide, written chemically as N2O, is a long-lived greenhouse gas that absorbs infrared radiation. It is released naturally and through human activities such as nitrogen-fertiliser use, manure management, biomass burning, and some industrial processes. Molecular nitrogen and oxygen are abundant atmospheric gases but are not significant greenhouse gases under normal conditions.

Correct answer: A. Amount of greenhouse gases can increase

Explanation: Factories and vehicles burn fuels and may release carbon dioxide, nitrous oxides, and other climate-relevant gases. If emissions exceed natural removal by oceans, vegetation, and other sinks, atmospheric concentrations can rise. This changes radiative forcing and may contribute to warming. The other options describe impossible or unrelated atmospheric outcomes.

Correct answer: A. Through higher energy use and vehicles

Explanation: Cities concentrate buildings, industries, transport, electricity demand, and waste generation. Burning fossil fuels for vehicles, heating, cooling, construction, and power production releases carbon dioxide and other greenhouse gases. Urban expansion can also reduce vegetation and carbon storage. Therefore, high energy use and vehicle dependence can increase a city's contribution to global warming.

Correct answer: A. They trap some heat in the atmosphere

Explanation: Greenhouse gases allow most incoming shortwave sunlight to pass through but absorb particular wavelengths of the longwave infrared radiation emitted by Earth's surface. They then re-radiate energy in all directions, including downward. This slows the loss of heat to space and warms the surface and lower atmosphere, forming the greenhouse effect.

Correct answer: A. Low-lying coastal areas

Explanation: Low-lying coastal areas are especially vulnerable to sea-level rise because they are only slightly above present sea level. Rising seas can cause coastal flooding, shoreline erosion, saltwater intrusion into soil and groundwater, and displacement of settlements and infrastructure. Densely populated deltas and small islands face particularly serious risks. High mountains, dry plateaus, and deep underground areas are not directly exposed to advancing seawater in the same way. Therefore, option A is correct.

Correct answer: A. Because both show a heat-trapping effect

Explanation: A glasshouse allows much of the Sun’s shortwave radiation to enter, while the warmed interior loses heat more slowly. The atmospheric greenhouse effect is an analogy: greenhouse gases such as carbon dioxide, methane, and water vapour absorb and re-emit outgoing longwave radiation, thereby warming the lower atmosphere. The atmosphere is not literally made of glass, so option A expresses the relevant comparison.