Why is coal gas not preferred for home use?

Coal gas is a mixture of gases, primarily hydrogen, methane, and carbon monoxide, produced from coal. Despite its high calorific value, it is not preferred for home use due to significant safety concerns.

Let's evaluate the given options:

• (A) burns explosively: Coal gas contains a high percentage of hydrogen, which is extremely flammable and forms explosive mixtures with air over a wide range of concentrations. This makes it highly dangerous for domestic use, as leaks can easily lead to catastrophic explosions.
• (B) has an unpleasant odour: While some components might have an odour, this is not the primary reason for its non-preference. Odorants can be added to odorless gases for safety.
• (C) contains pollutants: Coal gas contains toxic pollutants such as carbon monoxide (CO) and sulfur compounds. Carbon monoxide is highly poisonous and can be fatal even in small concentrations, making it a serious health hazard in homes. Sulfur compounds contribute to air pollution and have an unpleasant smell.
• (D) is more expensive than other fuel gases: While cost can be a factor, the primary reasons for not using a fuel in homes are usually safety and health concerns.

Both the explosive nature (A) and the presence of toxic pollutants like carbon monoxide (C) are major reasons why coal gas is not preferred for home use. However, the question asks for the reason. The explosive potential due to its high hydrogen content is a direct and immediate physical danger that can lead to widespread destruction and loss of life. This is a critical safety concern for any fuel used in a confined domestic environment.

The final answer is $\boxed{\text{A) burns explosively}}$.