In a balanced chemical equation, the number of molecules represented by the coefficients of each reactant and product must be equal. Therefore, the chemical or element with the largest coefficient in a balanced equation will have the largest number of molecules.

For example, consider the balanced equation for the combustion of methane:

CH₄ + 2O₂ → CO₂ + 2H₂O

In this equation, the coefficients indicate that 1 molecule of methane reacts with 2 molecules of oxygen to produce 1 molecule of carbon dioxide and 2 molecules of water. Since the coefficient for oxygen (2) is the largest in this equation, oxygen will have the largest number of molecules.