Which one of the following arrangements of molecules is correct on the basis of their dipole moments?

Which one of the following molecules is polar?

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 :-

Which molecule has a zero dipole moment?

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

Identify the set of molecules which are not in the correct order of their dipole moments.