Which molecule is nonpolar but has polar covalent bonds?

A molecule can have polar bonds, but it will be nonpolar if the bond dipoles cancel.  Example CO2             dipoles cancel out ; O=C=O

The problem here is that according to aufbau principle before 3d orbital 4s subshell comes.after filling 3p orbital with electrons you have 4 electrons left, you place two in 4s with opposite spin and the other two in 3d in any of its two orbitals of total five orbitals with the same spin.