Explanation:

When coal is burned, it undergoes a process called combustion, which is a chemical reaction between the carbon in the coal and oxygen in the air. This reaction releases heat energy in the form of light and heat.

Types of Combustion:

There are two types of combustion:

1. Complete Combustion: In this type of combustion, the fuel is burned in the presence of sufficient oxygen. It produces a blue flame and releases a large amount of heat energy.

2. Incomplete Combustion: In this type of combustion, the fuel is burned in the absence of sufficient oxygen. It produces a yellow or orange glow and releases less heat energy.

Why Coal Burns with Glow:

Coal contains impurities like sulfur and moisture, which can hinder the combustion process. When coal is burned, it undergoes incomplete combustion due to the presence of these impurities. This incomplete combustion results in the production of a yellow or orange glow instead of a blue flame.

Conclusion:

In conclusion, coal burns with only a glow due to the incomplete combustion process caused by the impurities present in it. This incomplete combustion results in the production of less heat energy and a yellow or orange glow.