Why do living organisms contain moe hydrogen atoms than any other atoms, yet 65% of a typical organisms mass is oxygen

The reason is that Oxygen atoms contain 16 times more mass than Hydrogen atoms.

Hydrogen  Has only one proton and no neutrons and so has an atomic number of 1 and a mass of 1

Oxygen  Has 8 protons and also 8 neutrons and so has an atomic number of 8 and a mass of 16.

It takes 16 Hydrogen atoms to equal the mass of 1 oxygen atom.

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