Answer
(a) Volume of cube is $8\,\mathrm{L}$.
(b) Mass of water in cube is $8\,\mathrm{kg}$.
Work Step by Step
(a) A cube with side $20\,\mathrm{cm}$ has volume -
$20^3$ = $8000\,\mathrm{cm^3}$ = $8000\,\mathrm{ml}$ = $8\,\mathrm{L}$.
(b) Density of water is $1\,\mathrm{g/cm^3}$.
Mass of water in cube is -
$\mathrm{volume}\times \mathrm{density}$ = $8000\times1$ = $8000\,\mathrm{g}$ = $8\,\mathrm{kg}$.
