UGC NET Questions (Paper – 1)

Wind energy harnesses the kinetic energy of moving air using turbines connected to generators. During operation, this process does not involve combustion and therefore does not release carbon dioxide, sulphur dioxide, particulates or other typical power-plant pollutants. While there are impacts associated with manufacturing and installation, the operational emissions are very low compared with coal-based thermal power. Hence, the absence of direct greenhouse gas and air pollutant emissions during operation is a key environmental advantage.

Option A:
Option A is correct because it highlights the major environmental benefit of wind power, namely low operational emissions. This makes wind a critical component of strategies aiming to decarbonise electricity systems and reduce local air pollution.

Option B:
Option B is incorrect since wind farms do require land or offshore space for turbine placement and access roads. Land-use planning is an important consideration in wind-energy development.

Option C:
Option C is incorrect because wind turbines do not consume coal; they replace the need for coal-based electricity generation. Suggesting they use coal misunderstands the technology.

Option D:
Option D is incorrect as wind can blow at any time of day depending on local weather patterns. Wind availability is variable, but it is not restricted to nighttime.

Statements A, B and C are correct and reflect the established link between energy choices and environmental outcomes. Fossil fuels emit carbon dioxide, efficiency measures cut demand and emissions and renewable sources help in mitigation. Statement D is clearly incorrect because energy policy is central to environmental protection through regulations, incentives and technology choices. Hence, the combination that includes A, B and C only is the correct answer.

Option A:
Option A is incorrect because it contains only A and B and ignores C. While A and B are accurate, C is also a correct statement since renewables contribute significantly to mitigation strategies. Leaving out a true statement makes the option incomplete.

Option B:
Option B is incorrect as it combines A, B and D and wrongly treats D as correct. By asserting that energy policy has no relevance for environmental protection, D contradicts the basic understanding of climate and energy governance. Including this false statement invalidates the option.

Option C:
Option C is incorrect because it groups A, C and D and again accepts D as valid. Although A and C are true, adding D undermines the environmental role of energy policy, so the option cannot be chosen.

Option D:
Option D is correct because it includes all the true statements—A, B and C—and excludes the false one. It recognises both the problems of fossil fuels and the solutions offered by efficiency and renewable energy. As a result, it fully satisfies the requirement of the question.

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.

The natural greenhouse effect keeps Earth warm enough for life by trapping some outgoing infrared radiation. Human activities such as burning fossil fuels and deforestation have increased greenhouse gas levels,leading to extra warming beyond this natural level. This extra warming is known as the enhanced greenhouse effect. Therefore enhanced is the correct word to complete the phrase in the stem.

Option A:
The natural greenhouse effect refers to the baseline warming that has always existed due to naturally occurring greenhouse gases. It is essential for maintaining habitable temperatures and is not the additional human induced component highlighted in the question.

Option B:
Moderate does not correspond to any widely recognised term in climate science. While the enhanced greenhouse effect may or may not be moderate, the established term focuses on the idea of being stronger than the natural effect,not moderate.

Option C:
Shielded greenhouse effect is not an accepted expression. Shielding would imply blocking radiation rather than trapping more of it. Thus this option does not fit the phenomenon described in the stem.

Option D:
Enhanced greenhouse effect clearly indicates that the original process has been intensified by human actions. It accounts for the observed trend of rising global temperatures and changing climate patterns,exactly what the question refers to.

Acid rain forms when sulphur dioxide and nitrogen oxides react with water vapour and other chemicals in the atmosphere to produce sulphuric and nitric acids. These acids then fall to the ground with rain, snow or dust. Because the stem mentions burning fossil fuels and industrial processes,the combination of sulphur dioxide and nitrogen oxides best explains the phenomenon.

Option A:
Carbon monoxide and ozone are important air pollutants, but they do not directly form strong acids responsible for acid rain. Carbon monoxide mainly affects human health, and tropospheric ozone is a component of photochemical smog. Therefore this pair does not match the primary chemical cause described.

Option B:
Sulphur dioxide and nitrogen oxides are released in large quantities from coal based power plants, industrial boilers and vehicles. Once in the atmosphere, they undergo oxidation and acid formation, leading to acid deposition. This clearly aligns with the explanation of acid rain in the question.

Option C:
Methane and ammonia can participate in atmospheric chemistry and contribute to other environmental issues such as eutrophication and greenhouse effects. However, they are not the principal precursors of acid rain in most contexts. Hence this option is not correct.

Option D:
Chlorofluorocarbons are associated mainly with ozone layer depletion, and helium is a chemically inert gas. Neither plays a significant role in generating acid rain, so this pair is inappropriate for the stem.