Calculate the no. of molecules in drop of water weighing 0.036 g.

Given mass = 0.036 g

Molar mass = 18 gm/mol

Number of moles= $\frac{Givenmass}{Molarmass}$

$\therefore Molesof{H}_{2}O=\frac{0.036}{18}=2\times {10}^{-3}$

$\therefore$ No. of molecules = $2\times {10}^{-3}\times 6.022\times {10}^{23}$

$=12.044\times {10}^{20}$ molecules