Multiple choice

Which of the following atoms is most abundant in living organism?

  1. Oxygen

  2. Carbon

  3. Hydrogen

  4. Nitrogen
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Hydrogen is the most abundant atom in living organisms by number, because water (H2O) makes up about 70% of cell mass, and hydrogen is present in almost all organic molecules. Oxygen is second most abundant by atom count, followed by carbon and nitrogen. By mass, oxygen is most abundant.

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