Pick out the molecule which has zero dipole moment.

Which of the following species represents a dipole-induced dipole interaction?

Arrange the following compounds in increasing order of their dipole moment :
$HBr$,$H_2S$,$NF_3$ and $CHCl_3$

For which molecules among the following,the resultant dipole moment $(\mu) \neq 0?$

Statement $I$: Dipole moment is a vector quantity and by convention it is depicted by a small arrow with tail on the positive centre and head pointing towards the negative centre.
Statement $II$: The crossed arrow of the dipole moment symbolizes the direction of the shift of charges in the molecules.
In the light of the above statements,choose the most appropriate answer from the options given below :-

$BF_3$ and $NF_3$ are both covalent molecules,but $BF_3$ is non-polar and $NF_3$ is polar. The reason for this is: