Which of the following molecules has a zero dipole moment?

If the dipole moment of chlorobenzene is $\mu$,what is the dipole moment of $1,3,5$-trichlorobenzene?

Which of the following molecules has a zero dipole moment?

Which of the following has the highest dipole moment?

If $HCl$ were purely ionic,its expected dipole moment would be $6.12 \, D$. However,the experimental dipole moment is $1.03 \, D$. Calculate the percentage ionic character. (in $\%$)

$(a)$ Discuss the significance/applications of dipole moment.
$(b)$ Represent diagrammatically the bond moments and the resultant dipole moment in $CO_2, NF_3$ and $CHCl_3$.