Which one is a polar molecule?

Among the following,the molecule with the lowest dipole moment is

Experiment shows that $H_2O$ has a dipole moment while $CO_2$ does not. Point out the structures which best illustrate these facts.

Which of the following molecules does not possess a permanent dipole moment?

Arrange the following compounds in the increasing order of their dipole moment.

If an $AB_3$ molecule (containing four atoms) has a dipole moment of zero and another has a non-zero dipole moment,what does this indicate about their shapes?