Which of the following statement is true regarding combustion?

It is a chemical process in which a substance reacts with oxygen to give off heat.

The correct answer is option 3. It is a chemical process in which a substance reacts with oxygen to give off heat.

A chemical process in which a substance reacts with oxygen to give off heat is called combustion.

The substance that undergoes combustion is said to be combustible. It is also called a fuel.

The fuel may be solid, liquid or gas.

Sometimes, light is also given off during combustion, either as a flame or as a glow.