GED Science Practice 2026 – 400 Free Practice Questions to Pass the Exam

The correct answer is carbon monoxide. This substance is a colorless and odorless gas that is produced when carbon-containing fuels do not burn completely. Because it is produced from the incomplete combustion of carbon, it can accumulate in enclosed spaces where there is inadequate ventilation, leading to potentially lethal consequences for those exposed to it. Carbon monoxide binds strongly to hemoglobin in the blood, which prevents oxygen from being transported effectively throughout the body, causing symptoms of poisoning that can result in severe health impacts or even death.

In contrast, carbohydrates are organic compounds made up of carbon, hydrogen, and oxygen, primarily serving as energy sources but not as gases involved in combustion processes. Carbon dioxide, while it is a gas produced during the complete combustion process, is not poisonous in the same way carbon monoxide is, as it is a natural byproduct of respiration and combustion. The term "cathode" refers to the electrode where reduction occurs in an electrochemical cell and is unrelated to combustion or the production of gases from burning fuels.