Question

The number of molecules having lone pair of electrons on central atom in the following is: BF$_3$, SF$_4$, SiCl$_4$, XeF$_4$, NCl$_3$, XeF$_6$, PCl$_5$, HgCl$_2$, SnCl$_2$

• A. 6
• B. 3
• C. 4
• D. 5

Hint:

Draw the Lewis structure to determine lone pairs on the central atom.

Answer 1

The Correct Option is D

Let's examine each molecule: BF$_3$: Boron has 3 valence electrons, all bonded to fluorine, leaving no lone pairs on boron.
SF$_4$: Sulfur has 6 valence electrons. Four are bonded to fluorine, and one lone pair remains on sulfur.
SiCl$_4$: Silicon has 4 valence electrons, all bonded to chlorine, leaving no lone pairs on silicon.
XeF$_4$: Xenon has 8 valence electrons. Four are bonded to fluorine, and two lone pairs remain on xenon.
NCl$_3$: Nitrogen has 5 valence electrons. Three are bonded to chlorine, and one lone pair remains on nitrogen.
XeF$_6$: Xenon has 8 valence electrons. Six are bonded to fluorine, and one lone pair remains on xenon.
PCl$_5$: Phosphorus has 5 valence electrons, all bonded to chlorine, leaving no lone pairs on phosphorus.
HgCl$_2$: Mercury has 2 valence electrons, both bonded to chlorine, leaving no lone pairs on mercury.
SnCl$_2$: Tin has 4 valence electrons. Two are bonded to chlorine, and one lone pair remains on tin.
The molecules with lone pairs on the central atom are SF$_4$, XeF$_4$, NCl$_3$, XeF$_6$, and SnCl$_2$. Therefore, there are 5 such molecules.