Correct Answer: Both assertion and reason are correct, and the reason is the correct explanation of the assertion.

Solution : The correct answer is (a) Both assertion and reason are correct, and the reason is the correct explanation of the assertion.

The assertion states that commercial energy sources are widely used for industrial production and transportation, which is correct. Commercial energy sources, such as fossil fuels (coal, oil, and natural gas), are commonly employed in various industries and transportation sectors to meet the high energy demands. These energy sources provide a reliable and efficient energy supply for powering manufacturing processes, operating machinery, and fueling vehicles used in transportation.

The reason provided states that commercial energy sources are more cost-effective and have higher energy density compared to non-commercial sources, and this is the correct explanation of the assertion. Commercial energy sources are preferred in industrial production and transportation due to their cost-effectiveness and high energy density. Fossil fuels, for example, are relatively inexpensive to extract and process, making them economically viable for large-scale energy consumption. Additionally, fossil fuels have high energy density, meaning they can release a significant amount of energy per unit of volume or weight. This makes them suitable for applications that require a concentrated and readily available energy source.

Therefore, both the assertion and reason are correct, and the reason serves as the correct explanation for why commercial energy sources are widely used for industrial production and transportation.