The following are some statements about dipole moment. The correct ones are
i) The dipole moment of all diatomic molecules is zero
ii) The dipole moment of a diatomic molecule having non-polar bonds is zero
iii) The dipole moment of a diatomic molecule having polar covalent bond is non-zero.
 

(i) Only homonuclear diatomic molecules have zero dipole moment. Ex: molecules such as Br₂ and N₂ have no difference in electronegativity, so their dipole moment is zero.

(ii) $$\begin{gathered} \begin{array}{c}\mathrm{O}=\mathrm{c}=0 \mathrm{non} \mathrm{plorar}\\ \end{array} \\ \mathrm{\mu }=0 \end{gathered}$$

(iii) dipole moment is due to the polarity of covalent bonds. Ex: HCl has non zero dipole moment.

Hence, the correct option is  (C)