How much combustion air is required to burn one cubic foot of natural gas completely?

To completely burn one cubic foot of natural gas, approximately 10 cubic feet of combustion air is required. This specific ratio stems from the stoichiometry of natural gas combustion, which primarily involves methane (CH₄). The combustion process requires a certain amount of oxygen to react with the fuel to produce carbon dioxide and water.

For complete combustion of methane, the ideal reaction can be summarized as follows:

[ CH₄ + 2 O₂ \rightarrow CO₂ + 2 H₂O ]

In this reaction, each molecule of methane reacts with two molecules of oxygen. Since air is composed of about 21% oxygen, the volume of air needed is significantly higher because only a fraction of air is oxygen.

Calculating approximately yields that to fully combust 1 cubic foot of natural gas, around 10 cubic feet of air is necessary. This consideration is crucial for ensuring efficient combustion and avoiding incomplete combustion, which can lead to dangerous byproducts like carbon monoxide.

The other options provided do not align with the combustion air requirement for natural gas, as they exceed or fall short of this necessary volume, leading to wasteful combustion or unsafe emissions.