Explanation

(c)
Dipole moment is a vector quantity. The dipole moment of symmetrical molecule is zero. Only the molecule which has distorted shape has dipole moment.
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$\because$ $CO_{2},\$p -dichlorobenzene and $CH_{4}$ have regular symmetrical shape.
$\therefore$ They don’t have dipole moment.
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$NH_{3}$ has distorted structure due to presence of lone pair of electron.
$\therefore$ It has dipole moment.