Which of the following compounds is non-polar?

The dipole moment is zero for the molecule:

The most polar bond is

The number of non-polar molecules from the following is . . . . . . $HF, H_2O, SO_2, H_2, CO_2, CH_4, NH_3, HCl, CHCl_3, BF_3$

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?

Assertion : Molecules of larger size have higher polarizability.
Reason : Polarizability is observed only in those molecules which have a permanent dipole moment.