Here's why:

* Combustion is a chemical process that involves the rapid reaction between a substance with an oxidant, usually oxygen, to produce heat and light.

* In this case, magnesium (Mg) reacts with oxygen (O2) in the air, producing magnesium oxide (MgO) along with heat and a bright white light.

Here's the chemical equation for the reaction:

2Mg + O2 → 2MgO