_____ is a colorless, odorless, nontoxic gas that is 1.5 times heavier than air.

_____ is a colorless, odorless, nontoxic gas that is 1.5 times heavier than air.

• A. Carbon dioxide
• B. Oxygen
• C. Nitrogen
• D. Helium

Answer: (A)

Understanding gas density relative to air helps explain why a gas with those properties points to carbon dioxide. A gas that is colorless, odorless, and considered nontoxic but heavier than air will tend to collect near the floor in enclosed spaces. Carbon dioxide matches this profile: it is colorless and odorless, generally regarded as non-toxic at typical exposure levels, and its density is about 1.5 times that of air, so it stays low. The other gases don’t fit this specific density clue as closely—oxygen is heavier than air but not about 1.5 times heavier, nitrogen is roughly the same as air, and helium is much lighter. So carbon dioxide is the best answer because its density relative to air aligns with the stated 1.5× heavier characteristic while still being colorless, odorless, and non-toxic.

Understanding gas density relative to air helps explain why a gas with those properties points to carbon dioxide. A gas that is colorless, odorless, and considered nontoxic but heavier than air will tend to collect near the floor in enclosed spaces. Carbon dioxide matches this profile: it is colorless and odorless, generally regarded as non-toxic at typical exposure levels, and its density is about 1.5 times that of air, so it stays low. The other gases don’t fit this specific density clue as closely—oxygen is heavier than air but not about 1.5 times heavier, nitrogen is roughly the same as air, and helium is much lighter. So carbon dioxide is the best answer because its density relative to air aligns with the stated 1.5× heavier characteristic while still being colorless, odorless, and non-toxic.