Question

which atmospheric gas is being described? second most abundant, composed of a diatomic molecule, humans need it to breathe. carbon dioxide sodium argon oxygen

Explanation:

• Carbon dioxide (\(CO_2\)) is not the second - most abundant gas in the atmosphere.
• Sodium (\(Na\)) is a solid metal at room temperature and not an atmospheric gas.
• Argon (\(Ar\)) is a noble gas. It is the third - most abundant gas in the atmosphere (about 0.93%), while oxygen (\(O_2\)) is the second - most abundant (about 21%). Also, \(O_2\) is a diatomic molecule (\(O - O\)) and is essential for human respiration.

Answer:

oxygen