Question 4
18 g of water contains 6.022 × 1023 molecules. What is the total number of atoms in it?
The right answer is the one marked above.
1.8066 × 1024. A water molecule has three atoms, so 6.022 × 1023 × 3 = 1.8066 × 1024.
6.022 × 1023 is the number of molecules, not of atoms. Multiplying by two instead of three gives 1.2044 × 1024, which is only the number of hydrogen atoms.