How many molecules of oxygen are needed to combust one molecule of fuel?

Combustion is a chemical reaction that typically involves a fuel reacting with oxygen to produce heat and light, along with carbon dioxide and water as byproducts. The stoichiometry of the combustion reaction depends on the specific fuel being used.

For many common fuels, like hydrocarbons (for example, methane, which has the chemical formula CH₄), the complete combustion reaction requires two molecules of oxygen. The general idea is that for every hydrocarbon fuel molecule, two molecules of oxygen react to produce carbon dioxide and water.

For methane, the balanced combustion reaction is:

CH₄ + 2 O₂ → CO₂ + 2 H₂O

In this example, you see that one molecule of methane requires two molecules of oxygen for complete combustion. This stoichiometry holds for many hydrocarbons or similar fuels, making two molecules of oxygen a common requirement in combustion processes.

Therefore, when considering the combustion of typical fuels, the correct answer is that two molecules of oxygen are necessary to combust one molecule of fuel, as accurately identified.