Question

Identify a molecule having highest number of lone pair of electrons in valence shell of central atom.

• A. $\text{NH}_3$
• B. $\text{SF}_4$
• C. $\text{ICl}_3$
• D. $\text{PCl}_3$

Hint:

Halogen central atoms (Group 17) usually have the most lone pairs because they have 7 valence electrons to start with.

Answer 1

The Correct Option is C

Step 1: Concept
The number of lone pairs is determined by the group number of the central atom and the number of bonds it forms.

Step 2: Meaning
$\text{Lone Pairs} = \frac{(\text{Valence electrons} - \text{Bonds})}{2}$.

Step 3: Analysis
- (A) $\text{NH}_3$: N (Group 15, 5 e-), 3 bonds. LP $= (5-3)/2 = 1$. - (B) $\text{SF}_4$: S (Group 16, 6 e-), 4 bonds. LP $= (6-4)/2 = 1$. - (C) $\text{ICl}_3$: I (Group 17, 7 e-), 3 bonds. LP $= (7-3)/2 = 2$. - (D) $\text{PCl}_3$: P (Group 15, 5 e-), 3 bonds. LP $= (5-3)/2 = 1$.

Step 4: Conclusion
$\text{ICl}_3$ has the highest number (2) of lone pairs on the central atom. Final Answer: (C)