Which is the most abundant gas in earth’s atmosphere? nitrogen water vapor carbon dioxide oxygen

The answer is Nitrogen.

Over 78 percent of the air we breathe is made up of nitrogen, about 20 percent is oxygen. The remaining two percent is made of carbon dioxide, carbon monoxide, argon, and water vapor.

hydrogen is a compound or a single element and a element is a pure substence that cannot be separated into simpler subtances

clorine is a compound its a chemical substance that forms when two or more different elements combine

so both hydrogen and clorine are compounds