Question

Calculate the number of water molecules present in one drop of water which weighs $0.18g$.

Answer 1

Molecular mass of $H_O=18g=1mole$

$18g$ of water contains $6.022\times {10}^{23}$ molecules.

$\therefore 0.18g$ of water contains, $=\frac{0.18\times 6.023\times {10}^{23}}{18}=0.06023\times {10}^{23}=6.023\times {10}^{23}\text{molecules}$.