Match Bond Pair and Lone Pair on Central Atom

 

❓ Question

Match the following molecules/ions with the ratio:

$$\text{Bond pair : Lone pair}$$

(on the central atom)

Molecule/Ion	Ratio Options
A. $ICl_2^-$	I. $4:2$
B. $H_2O$	II. $4:1$
C. $SO_2$	III. $2:3$
D. $XeF_4$	IV. $2:2$

---

🖼 Question Image

---

✍️ Short Concept

Golden rule:

👉 Count only sigma bonds on central atom
👉 Double bond counts as ONE bond pair

Then count lone pairs.

---

🔷 Step 1 — $ICl_2^-$ 💯

Iodine valence electrons:

$$7 + 1 = 8$$

Structure:

• 2 bond pairs
• 3 lone pairs

So:

$$\boxed{2:3}$$

Hence:

$$A \rightarrow III$$

---

🔷 Step 2 — $H_2O$

Oxygen valence electrons:

$$6$$

Structure:

• 2 bond pairs
• 2 lone pairs

So:

$$\boxed{2:2}$$

Hence:

$$B \rightarrow IV$$

---

🔷 Step 3 — $SO_2$

Sulfur central atom:

👉 Two sigma bonds
👉 One lone pair

So:

$$\boxed{2:1}$$

This corresponds to option II.

Hence:

$$C \rightarrow II$$

---

🔷 Step 4 — $XeF_4$

Xenon valence electrons:

$$8$$

Structure:

• 4 bond pairs
• 2 lone pairs

So:

$$\boxed{4:2}$$

Hence:

$$D \rightarrow I$$

---

✅ Final Answer

$$\boxed{ A-III,\; B-IV,\; C-II,\; D-I }$$

---

⭐ Golden JEE Insight

Most common mistake:

❌ Counting double bond as two bond pairs

Correct rule:

$$\boxed{\text{Double bond = one sigma bond}}$$

Only sigma bonds decide bond-pair count.