Which gas is NOT commonly found in smoke?

Oxygen is not commonly found in smoke due to the combustion process. When materials burn, they consume oxygen to support the fire. As the fuel burns, it generates a variety of gases and particulate matter, including carbon monoxide, hydrogen cyanide, and soot. These substances are products of incomplete combustion and result from organic materials and other hydrocarbons breaking down under heat.

In contrast, as a fire consumes oxygen, the atmosphere surrounding it becomes depleted of this gas. Therefore, while carbon monoxide, hydrogen cyanide, and soot can be present in smoke due to the byproducts of burning materials, oxygen levels in smoke tend to be significantly lower, making it an uncommon component in smoke.