Which of the following is not a normal combustion product of natural gas?

Ferrous oxide is not a normal combustion product of natural gas because the primary products of a complete combustion reaction involving natural gas, which is primarily methane (CH₄), include carbon dioxide, water vapor, and heat. During combustion, methane reacts with oxygen to produce carbon dioxide and water, while also releasing energy in the form of heat.

In contrast, ferrous oxide, or iron(II) oxide, is a compound that typically forms from the oxidation of iron rather than from the combustion of organic gases like natural gas. It is not a standard byproduct of combustion processes involving hydrocarbons. This distinction is key in understanding the chemical reactions during combustion and the expected outcomes of burning natural gas.