Which of the following is not treated as a commercial source of energy in the modern economy?

Introduction / Context:

This question tests basic understanding of energy economics, specifically the distinction between commercial and non commercial sources of energy. In development and planning, energy sources are often grouped according to whether they are bought and sold in the market. Knowing which sources are considered commercial is important for analysing energy statistics and policies.

Given Data / Assumptions:

• Commercial energy sources are those that are traded in the market and have a well defined price.
• Non commercial or traditional sources are usually collected and used directly without being formally marketed.
• Options include coal, petroleum, natural gas, firewood and electricity from thermal power plants.
• We assume a standard classification used in basic economics and geography textbooks.

Concept / Approach:

Commercial energy consists of sources like coal, petroleum, natural gas and commercial electricity which are produced, distributed and sold through formal markets. Non commercial energy generally includes fuelwood, agricultural waste and animal dung collected by households for domestic use. The approach is to identify which option falls into the traditional, largely non marketed category rather than the industrial, traded category.

Step-by-Step Solution:

Verification / Alternative check:

Economic surveys and planning documents in many countries separate energy into commercial and non commercial categories. They usually list coal, lignite, petroleum, natural gas and commercial electricity under commercial energy. Under non commercial energy they include fuelwood, agricultural residues and animal dung cakes. This consistent classification across reference materials confirms that firewood is not treated as a commercial source of energy in the usual sense.

Why Other Options Are Wrong:

Coal is sold to power plants, industries and sometimes households through markets, so it clearly belongs to commercial energy. Petroleum products such as petrol, diesel and kerosene are sold at fuel stations and have regulated prices, making them classic commercial fuels. Natural gas is also a marketed fuel supplied through pipelines or cylinders. Electricity generated in thermal power plants is sold to consumers and industries via distribution companies and is paid for according to metered use. Therefore these options are all commercial sources.

Common Pitfalls:

Students sometimes think that any source which can be sold anywhere is commercial, and point out that firewood is also sold in some urban markets. However, the classification in basic textbooks is based on the dominant pattern of use in traditional rural settings, where firewood is mostly collected, not bought. Another pitfall is to overlook natural gas or electricity because they are less visible as fuels, but both are major commercial energy sources. Remembering the textbook distinction helps avoid these confusions.

Final Answer:

The item that is generally not treated as a commercial source of energy is Firewood.