Question

How many hydrogen atoms are present in each water molecule?

Answer 1

2 atoms.
The chemical formula for water is H20 which means that every molecule of water has 2 atoms of hydrogen (H) and one atom of oxygen (O).

Answer 2

This answer is obtained from the formula of the molecule.

That is what a molecular formula means: it provides the number of atoms of each element in a molecule.

The molecular fomula of water is widely known:
`H_(2)O`

The you know from that that one molecule of water has two atoms of hydrogen and one atom of oxygen.

Answer: There are two atoms of hydrogen in each water molecule.