The dipole moment is zero for the molecule:

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: $NH_3$ and $NF_3$ molecules have a pyramidal shape with a lone pair of electrons on the nitrogen atom. The resultant dipole moment of $NH_3$ is greater than that of $NF_3$.
Reason $R$: In $NH_3$,the orbital dipole due to the lone pair is in the same direction as the resultant dipole moment of the $N-H$ bonds. $F$ is the most electronegative element.

Which of the following compounds will show a dipole moment?

Which of the following substances has the lowest dipole moment?

Which of the following substances has the highest dipole moment?

Both $BF_3$ and $NH_3$ are covalent molecules. However,$BF_3$ is non-polar while $NH_3$ is polar. What is the reason for this?