Unbalanced equation:

CO + O₂ → CO₂

Balanced equation:

2CO + O₂ → 2CO₂

Explanation:

* Carbon (C): There's one carbon atom on each side, so it's already balanced.

* Oxygen (O): There are two oxygen atoms on the left (one in CO and two in O₂) and two oxygen atoms on the right (in CO₂). To balance the oxygen, we need a coefficient of 2 in front of CO.

Therefore, the coefficient value for CO is 2 to balance the reaction.