Question

which gas in earths atmosphere helps living things make proteins?
oxygen
nitrogen
water vapor
carbon dioxide

Explanation:

Proteins are made up of amino acids, and amino acids contain nitrogen. Nitrogen gas (\(N_2\)) in the atmosphere is converted into forms (like ammonia \(NH_3\)) that can be used by living organisms to synthesize proteins through processes like nitrogen fixation. Oxygen (\(O_2\)) is mainly used for respiration. Water vapor (\(H_2O\)) is involved in hydration and some biochemical reactions but not a key element in protein structure. Carbon dioxide (\(CO_2\)) is used in photosynthesis (to make carbohydrates) not directly for protein synthesis.

Answer:

nitrogen