Question

How many moles of hydrogen atoms are present in 25.0 g of water?

Answer 1

Moles of water =25/18
1 mole of water contain 2 moles of hydrogen
Therefore 25/18 moles of water contain 50/18 mole of H

Answer 2

Answer: There are 2.77 moles of hydrogen in 25 g of water.

Explanation:

$Moles=\frac{\text{Given mass}}{\text{Molar mass}}$

moles of water=$\frac{25.0g}{18g/mol}=1.39moles$  

1 mole of $H_2O$ contains = 2 moles of hydrogen

Thus 1.39 moles of $H_2O$ contains =$\frac{2}{1}\times 1.39=2.77moles$ of hydrogen.

Thus there are 2.77 moles of hydrogen in 25 g of water.