(A) 2:1
(B) 1:2
(C) 8:1
(D) 1:8
The answer is: (C) 8:1
The chemical formula of water is H2O. The atomic mass of hydrogen is 1, and the atomic mass of oxygen is 16. So, the ratio of oxygen and hydrogen by mass is 16:2 or 8:1. Here, there are two atoms of hydrogen and one atom of oxygen.