Which gas is colorless, odorless, and incombustible and is formed during respiration, combustion, and organic decomposition?

• A. Carbon dioxide
• B. Carbon monoxide
• C. Cartridge (firearms)
• D. Cast-off

Answer: (A)

The gas that matches these clues is carbon dioxide. It is produced during respiration when cells exhale CO2, during combustion as fuels burn, and during the breakdown of organic matter. It is colorless and odorless, and it does not support combustion, which means it is incombustible. This combination of properties distinguishes it from other gases. For example, carbon monoxide is also colorless and odorless, but it is not incombustible—it can form from incomplete combustion and can ignite under certain conditions; plus, it’s toxic rather than simply being non-flammable. The remaining options aren’t gases formed in these processes at all.