1 molecule of C3H7O has 7 atoms of hydrogen (remember that the numbers to the right of each symbol ara subscripts and they indicate the number of atoms of that element in the molecular formula).
Then 5 molecules will have 5 * 7 atoms of hydrogen.
5 * 7 = 35.
Then the answer is that there are 35 atoms of hydrogen in 5 molecules of isopropyl alcohol, C3H7O
