Question

Which of the following is a polar molecule?
(A) $Xe{F_4}$
(B) $B{F_3}$
(C) $S{F_4}$
(D) $Si{F_4}$

Answer 1

Polar molecules are asymmetric, either containing a lone pair of electrons on a central atom. Non-polar molecules are symmetric compounds that mean all of the sides around the central atom are identically bonded to the same element with no unshared pairs of electrons.

Complete step by step solution:
First of all let us talk about polar and nonpolar molecules.
Lone pair: The pair of electrons that are present in the valence shell but do not take part in the formation of molecules.
Polar molecules are asymmetric, either containing a lone pair of electrons on a central atom. For example: carbon tetrachloride, boron trifluoride. Here we can see in the molecule carbon tetrachloride the central metal atom is carbon and the surrounding atoms are chlorine and all the chlorine atoms are the same. Hence they are polar molecules.
Non-polar molecules are symmetric compounds that mean all of the sides around the central atom are identically bonded to the same element with no unshared pairs of electrons. For example: hydrogen fluoride. Here we can see in the molecule hydrogen fluoride the central metal atom is hydrogen and the surrounding atom is fluorine and the difference between their electronegativity. Hence they are nonpolar molecules.
Now we are given the compound $Xe{F_4}$ , $B{F_3}$ , $S{F_4}$ and $Si{F_4}$ . Now among these compounds we can see $Xe{F_4}$ , $B{F_3}$ and $Si{F_4}$ are non-polar molecules because the lone pair cancel each other's effect and the same atoms cancel their effect.
And the molecule $S{F_4}$ is polar in nature because in this there is only one lone pair in this which cannot be canceled by others.
Hence option C is correct.

Note:
Dipole moment: It is defined as the product of charge (a system in which two opposite charges separated by a certain distance) and the distance between opposite charges, is known as dipole moment.