Which of the following molecules has a zero dipole moment?

The observed dipole moment of $HCl$ is $1.303 \ D$. This indicates that $HCl$ has $17 \%$ ionic and $83 \%$ covalent character. The bond length of $HCl$ is $1.26 \ \mathring{A}$ and the charges on $H$ and $Cl$ ions are $+e$ and $-e$. Calculate the theoretical dipole moment in $D$.

Which of the following molecules has a zero dipole moment?

Given below are two statements:
Statement-$I$: Since fluorine is more electronegative than nitrogen,the net dipole moment of $NF_3$ is greater than $NH_3$.
Statement-$II$: In $NH_3$,the orbital dipole due to lone pair and the dipole moment of $N-H$ bonds are in opposite direction,but in $NF_3$ the orbital dipole due to lone pair and dipole moments of $N-F$ bonds are in same direction.
In the light of the above statements,choose the most appropriate from the options given below.

Match the following:

List-$I$ (Molecule)	List-$II$ (Dipole moment in $D$)
$A. HCl$	$I. 1.07$
$B. NH_3$	$II. 1.85$
$C. H_2O$	$III. 0.23$
$D. NF_3$	$IV. 1.47$

The correct answer is

The cyanide ion,$CN^{-}$ and $N_2$ are isoelectronic. But in contrast to $CN^{-}$,$N_2$ is chemically inert because of