Which of the following describes carbon monoxide?

• A. Tasteless, odorless, colorless, combustible, poisonous
• B. Has a strong odor
• C. Visible as a blue-green gas
• D. Non-toxic under any exposure

Answer: (A)

Carbon monoxide dangers come from how it behaves in the body and how hard it is to notice without equipment. It is tasteless, odorless, and colorless, so people can be exposed without realizing it. Its toxicity comes from binding to hemoglobin in the blood much more readily than oxygen does, forming carboxyhemoglobin and preventing oxygen from reaching tissues. That hidden, toxic nature is why this description—tasteless, odorless, colorless, poisonous—best captures what CO is like. The other statements are not true: CO does not have a strong odor, it is not seen as a blue-green gas, and it is not non-toxic.