UGC NET Questions (Paper – 1)

Statements A, B, D and E are correct and consistent with basic climate science. Statement A correctly lists major anthropogenic greenhouse gases, statement B explains how they trap outgoing long-wave radiation, statement D points to human-induced enhancement of global warming and statement E recognises the protective role of stratospheric ozone. Statement C is incorrect because the natural greenhouse effect is essential for maintaining Earth’s mean temperature at a habitable level. Therefore, the only combination that includes all true statements while excluding the false one is A, B, D and E.

Option A:
Option A is incorrect because it includes A, B and D but omits E. While A, B and D are indeed correct statements, E is also correct as stratospheric ozone shields living organisms from harmful ultraviolet radiation. By leaving out a true statement, this option does not fully capture the set of correct statements.

Option B:
Option B is correct because it includes statements A, B, D and E, all of which are scientifically accurate. It excludes statement C, which falsely portrays the greenhouse effect as entirely harmful and ignores its natural role in maintaining habitable temperatures. Hence, this option represents the complete and precise set of correct statements asked for in the question.

Option C:
Option C is incorrect because it adds statement C to the set of otherwise correct statements A, B and D. Statement C is wrong since the greenhouse effect in its natural form is beneficial and only its anthropogenic enhancement is problematic. Including a false statement makes this combination unacceptable.

Option D:
Option D is incorrect because it combines B, C, D and E. Although B, D and E are correct, the presence of statement C, which misrepresents the greenhouse effect as wholly harmful, makes the entire combination wrong. A valid answer must exclude all incorrect statements.

Statements A, B, D, E and F are all correct and together explain which gases are important, how the enhanced greenhouse effect works and how radiation is trapped. Carbon dioxide is the main long-lived anthropogenic gas, methane is more potent per unit mass, water vapour is a feedback gas and greenhouse gases absorb outgoing longwave radiation. Statement C is false because nitrous oxide and many fluorinated gases are well-known greenhouse gases with significant warming effects. Therefore, the combination that includes A, B, D, E and F only is correct.

Option A:
Option A is incorrect because it leaves out F and therefore fails to mention the basic physical mechanism of longwave absorption by greenhouse gases. Without F, the explanation of how warming actually occurs remains incomplete.

Option B:
Option B is correct as it lists all the true statements and excludes only C, which denies the greenhouse role of nitrous oxide and fluorinated gases. It provides a conceptually coherent description of greenhouse gases and the enhanced greenhouse effect.

Option C:
Option C is incorrect since it includes C, which is demonstrably wrong, and omits B, thereby losing the point about methane’s higher warming potential. This mixture of errors and omissions makes it unsuitable as the correct answer.

Option D:
Option D is incorrect because it omits A, ignoring the central role of carbon dioxide, while also excluding A’s emphasis on the primary anthropogenic driver. It also contains only a subset of true statements and thus does not fully characterise greenhouse gas behaviour.

Greenhouse gases are those that can absorb and emit infrared radiation, contributing to the greenhouse effect. Carbon dioxide from fossil fuels and deforestation, methane from agriculture and waste, and nitrous oxide from fertilisers are key anthropogenic drivers of current climate change. They have increased significantly in concentration since the industrial revolution.

Option A:
Option A is incorrect because nitrogen, oxygen and argon are major components of air but are not strong greenhouse gases under normal conditions.

Option B:
Option B is correct as it lists three important long-lived greenhouse gases recognised in international climate agreements.

Option C:
Option C is incorrect since neon, helium and krypton are inert gases with negligible greenhouse effect.

Option D:
Option D is incorrect because hydrogen, neon and argon are not principal contributors to observed warming.

Carbon dioxide is the primary greenhouse gas emitted by human activities,especially from burning fossil fuels for electricity,transport and industry. Its long atmospheric lifetime and high volume make it the dominant driver of anthropogenic climate change. The stem explicitly links the gas to combustion of coal,oil and natural gas,which clearly points to carbon dioxide. Hence Option A is correct.

Option A:
Carbon dioxide concentrations have been rising steadily since the industrial revolution,enhancing the greenhouse effect. Because of this central role,international climate agreements focus heavily on reducing CO₂ emissions. This explanation fits the description in the question.

Option B:
Methane is also a potent greenhouse gas and arises from agriculture,fossil fuel extraction and waste,but its global emissions from burning fossil fuels are smaller in volume than CO₂. It is therefore not the most significant gas in the specific context described.

Option C:
Ozone acts as a greenhouse gas in the troposphere but is not emitted directly in large amounts from fossil fuel combustion. It is mainly formed as a secondary pollutant,so it does not match the stem as closely as carbon dioxide.

Option D:
Carbon monoxide is a toxic gas produced by incomplete combustion and has health impacts,but its direct greenhouse effect is relatively weak compared to CO₂. Thus it is not the best answer here.

Carbon dioxide is the most significant anthropogenic greenhouse gas in terms of total emissions. It is released in large quantities through burning coal,oil and natural gas and through deforestation. Its long atmospheric lifetime and high volume make it the main driver of human induced climate change. Therefore carbon dioxide best fits the description in the question.

Option A:
Oxygen is a major component of the atmosphere but it is not a greenhouse gas. It does not trap outgoing infrared radiation in the way greenhouse gases do. Hence it cannot be the primary greenhouse gas mentioned in the stem.

Option B:
Nitrogen makes up the largest fraction of Earth’s atmosphere. However it is largely inert and does not act as a greenhouse gas in its diatomic form. Therefore it is not responsible for the described warming effect.

Option C:
Ozone in the troposphere acts as a greenhouse gas and pollutant,but its concentration is much lower than that of carbon dioxide. It is important locally but is not the primary anthropogenic greenhouse gas globally. Thus it is not the best answer here.

Option D:
Carbon dioxide is produced by combustion processes in power plants,industry and transport as well as by land use changes. It accumulates in the atmosphere and enhances the greenhouse effect. This makes it the central gas referred to in the question.