Question

the nitrogen cycle
atmospheric gases
gases in the atmosphere
other 1%
19%
80%
which gas makes up around 19% of the atmosphere and is the component that humans use directly?
argon
oxygen
carbon dioxide
ozone

Explanation:

Earth's atmosphere is ~19-21% oxygen, which humans directly inhale for respiration. Argon, carbon dioxide, and ozone do not match the 19% proportion or direct human use requirement.

Answer:

B. oxygen