UGC NET Questions (Paper – 1)

Primary energy sources are found in nature and have not yet undergone any conversion or transformation process. Coal dug directly from mines is a primary energy source because it is used in its original form for combustion. In contrast, electricity, petrol and hydrogen are secondary forms of energy obtained by processing or converting primary sources. Therefore, coal as extracted from mines is correctly identified as a primary source, as stated in Option C.

Option A:
Option A is incorrect since electricity from coal is a secondary energy form; it results from converting the chemical energy in coal into electrical energy through generation processes.

Option B:
Option B is incorrect because petrol is produced in refineries by processing crude oil. It is a secondary product derived from the primary fossil resource, not a primary energy source itself.

Option C:
Option C is correct because coal in the ground or freshly mined represents a natural energy resource that can be used directly for heating or electricity generation, illustrating its status as primary energy.

Option D:
Option D is incorrect because hydrogen produced by electrolysis depends on electricity, which is itself generated from primary sources. In this context, hydrogen is a secondary energy carrier, not a primary source.

Renewable energy sources are those that are replenished naturally on a human time scale and are not depleted by regular use. Solar energy is derived from sunlight, which is essentially inexhaustible for human purposes. Using solar energy reduces dependence on fossil fuels and lowers greenhouse gas emissions. Therefore, solar energy is correctly identified as a renewable source, making option A correct.

Option A:
Option A is correct because solar energy relies on the continuous flow of solar radiation, which is naturally replenished each day. It does not get exhausted like fossil fuels and is considered a key pillar of sustainable energy transitions.

Option B:
Option B, coal, is a fossil fuel formed over millions of years and is non-renewable on human time scales. Once extracted and burnt, it cannot be quickly replaced.

Option C:
Option C, petroleum, is also a fossil fuel that is finite and non-renewable. Its extraction and use contribute significantly to air pollution and climate change.

Option D:
Option D, natural gas, while cleaner than coal and oil in terms of emissions, is still a fossil fuel and non-renewable. It also releases carbon dioxide when burned and can leak methane during extraction and transport.

Nuclear power plants produce relatively low direct carbon emissions during normal operation. However, they generate radioactive wastes that remain hazardous for very long periods. Ensuring safe storage, transport and ultimate disposal of this waste poses technical, financial and institutional challenges. Thus, the long-term management of radioactive waste is widely recognised as a major environmental and health concern linked to nuclear power generation.

Option A:
Option A is incorrect because nuclear plants emit far less carbon dioxide than fossil fuel plants per unit of energy produced. While there are emissions in construction and fuel processing, large direct CO₂ release is not their defining environmental problem.

Option B:
Option B is incorrect since sulphur dioxide and soot are characteristic emissions from coal and oil combustion. Properly operated nuclear reactors do not release these pollutants in stack gases.

Option C:
Option C is incorrect because although nuclear plants require significant cooling water, they are usually sited and managed to avoid completely depleting groundwater resources. Water use is an issue but not the unique long-term hazard compared with radioactive waste.

Option D:
Option D is correct as it points to the persistent hazard of long-lived radionuclides. Safe containment must be maintained over time scales far exceeding normal infrastructure lifetimes, making this a central issue in debates over nuclear energy.