(c) $1 mole= 6.023 \times 10^{23} molecule$ $18 g = 6.02 \times 10^{23} molecule$ 18 g = mass of $6.02 \times 10^{23}$ water molecules Mass of one water molecule $= \frac {18}{6.023\times 10^{23}} g$ Density $ = 1 \, g \, cm^{-3}$ $Volume = \frac {Mass \, of \, one \, water \, molecule}{Density}$ $= \frac {18}{6.023 \times 10^{23} \times1 } = cm^3$ $\simeq 3.0 x 10^{-23} cm^3$