Explanation

(c)
The molecules having distorted geometry have dipole moment and those having regular geometry have zero dipole moment.
$\because\ {NH}_{3},\ {CH}_{3}Cl\ and\ {ClO}_{2}$ have distorted geometry.
$\therefore$ They have dipole moment.
$\because$ $BF_{3}$ has regular triangular planar geometry.
The dipole moment of $BF_{3}$ is zero.