Which one of the following is considered a commercial source of energy commonly used in households and industries?

Introduction / Context:
This question lies in the area of sources of energy and environmental science. It distinguishes between commercial and non commercial sources of energy. Commercial energy sources are those that are bought and sold in the market and form the backbone of modern energy supply systems. Non commercial sources are typically traditional or freely available sources often used in rural settings. You are asked to identify which option is a commercial source of energy from the list given.

Given Data / Assumptions:
Agricultural waste refers to crop residues and biomass left over from farming activities.
Dried dung is animal dung used as fuel after drying, often in rural households.
The Sun is the ultimate natural source of solar energy, but direct sunlight is not usually bought or sold as a fuel in the traditional sense.
Natural gas is a fossil fuel extracted, processed and distributed through pipelines or in cylinders for domestic and industrial use.
We assume standard textbook definitions of commercial and non commercial energy sources.

Concept / Approach:
Commercial energy sources are characterised by organised production, distribution and sale, and include fossil fuels such as coal, petroleum and natural gas, as well as electricity. Non commercial sources like firewood, agricultural waste and dried dung are often collected locally and used without entering formal markets. The Sun provides solar energy, which can be harnessed commercially through photovoltaic systems, but the direct resource itself is not typically treated as a purchased fuel. Natural gas, on the other hand, is clearly traded, billed and delivered as a commercial energy source, used for cooking, heating and power generation.

Step-by-Step Solution:
Step 1: Evaluate agricultural waste. It is often used as a traditional form of biomass fuel in rural areas and is usually not purchased on a large commercial scale; it is considered non commercial energy. Step 2: Evaluate dried dung. Like agricultural waste, dried dung is traditionally used in rural households and is generally not part of formal commercial energy markets, so it is also non commercial. Step 3: Evaluate the Sun. The Sun is the source of solar energy, but sunlight itself is not purchased as a fuel. While solar power installations are commercial, the direct energy source is not classified as a commercial fuel in the same sense as gas or coal. Step 4: Evaluate natural gas. Natural gas is extracted from wells, processed, and sold through companies to consumers and industries, making it a clear example of a commercial energy source. Step 5: Therefore, among the given options, natural gas is the correct answer as a commercial source of energy.

Verification / Alternative check:
Energy resource classifications in textbooks and economic reports typically list coal, petroleum products, natural gas and electricity as commercial energy sources because they are traded and priced in organised markets. In contrast, firewood, agricultural waste and animal dung are labelled as non commercial or traditional sources. Solar energy is recognised as a renewable commercial energy form when harnessed by solar panels and sold as electricity, but the direct Sun option in this question is not meant in that technological sense. These standard classifications confirm that natural gas is the commercial energy source among the choices given.

Why Other Options Are Wrong:
Agricultural waste is incorrect because it is generally collected and used locally without a formal commercial market, so it is considered a non commercial energy source.
Dried dung is wrong because, like agricultural waste, it is mostly used in rural households without entering the organised energy market and is thus non commercial.
The Sun is wrong in the context of this question because, although solar energy can be harnessed commercially, the Sun listed as a source here refers to the natural resource, not a traded fuel like natural gas.

Common Pitfalls:
Students may be tempted to choose the Sun because solar energy is increasingly important and modern. However, the question emphasises commercial sources of energy in the conventional sense of fuels and supply systems. Another pitfall is failing to distinguish between local traditional fuels and large scale commercial energy resources. Remembering that commercial energy is typically bought and sold through companies for domestic and industrial use helps to identify natural gas as the correct option.

Final Answer:
The commercial source of energy among the options given is Natural gas.