Q.20. Which of the following is a polar molecule?
(1) $S{F}_4$
(2) $Si{F}_4$
(3) $Xe{F}_4$
(4) $B{F}_3$

Dear student,
SiF₄ and BF₃ have regular tetrahedral and trigonal planar shape respectively and all regular structures have zero dipole moment. In XeF₄ it has square planar geometry which also makes it having a zero dipole moment. In SF₄ the molecule is having see-saw geometry since sulphur has 4 electrons bonded to 4 Fluorine atoms and has a lone pair left thereby making it sp³d hybridized which is not a regular structure since equatorial Fluorine cannot cancel the moment generated by lone pair and therefore SF₄ is a polar molecule.

Hence answer is (1)

Hope it helps
Regards