Which one of the following molecules has a zero dipole moment?

Identify the correct set of molecules with zero dipole moment.

Which of the following is a polar compound?

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.

Among the following compounds,the one which shows the highest dipole moment is

Which bond angle $\theta$ would result in the maximum dipole moment for the triatomic molecule $XY_2$ shown below?