Question

in the box provided explain why living organisms contain more hydrogen atoms than any other atoms, yet 65% of a typical organisms mass is oxygen.

Explanation:

Hydrogen atoms are small and light. While there are many of them, oxygen atoms have a much greater atomic mass. For example, in water ($H_2O$), there are 2 hydrogen atoms and 1 oxygen atom. The atomic mass of hydrogen ($H$) is approximately $1\ g/mol$, and the atomic mass of oxygen ($O$) is approximately $16\ g/mol$. In a water molecule, the mass contribution of hydrogen is $2\times1 = 2\ g/mol$, and the mass contribution of oxygen is $16\ g/mol$. Since water is a major component of living organisms, the higher atomic mass of oxygen leads to it contributing more to the mass of the organism despite there being more hydrogen atoms.

Answer:

Hydrogen atoms are small and light. Oxygen has a much greater atomic mass. In water (a major component of organisms), the higher atomic mass of oxygen makes it contribute more to mass despite more hydrogen atoms.