Which of the following is a polar molecule?

Polarity depends on molecular geometry and whether bond dipoles cancel out.${\text{BF}}_3$: Trigonal planar, dipoles cancel ($\mu =0$).${\text{SiF}}_4$: Tetrahedral, dipoles cancel ($\mu =0$).${\text{XeF}}_4$: Square planar, dipoles cancel ($\mu =0$).${\text{SF}}_4$: See-saw geometry (due to one lone pair). The bond dipoles do not cancel, resulting in a net dipole moment ($\mu \ne 0$).