Question

Number of compounds with one lone pair of electrons on central atom amongst following is
\(CIF_3, XeO_3, BrF_5, XeF_4, O_3, NH_3\),\( H_2O\)

Answer 1

Correct Answer: 4

1. CIF₃ (Chlorine trifluoride)

Chlorine (Cl) has 7 valence electrons. It forms 3 bonds with F atoms → uses 3 electrons. Remaining = 7 – 3 = 4 electrons = 2 lone pairs. 
→ **2 lone pairs on Cl**

2. XeO₃ (Xenon trioxide)

Xenon (Xe) has 8 valence electrons. Each oxygen forms a double bond, using 6 electrons in total (3 × 2). Used 6 electrons → 8 – 6 = 2 electrons = 1 lone pair. 
→ **1 lone pair on Xe**

3. BrF₅ (Bromine pentafluoride)

Bromine (Br) has 7 valence electrons. Forms 5 bonds with F → uses 5 electrons. Remaining 7 – 5 = 2 electrons = 1 lone pair. 
→ **1 lone pair on Br**

4. XeF₄ (Xenon tetrafluoride)

Xenon (Xe) has 8 valence electrons. Forms 4 bonds with F → uses 4 electrons. Remaining 8 – 4 = 4 electrons = 2 lone pairs. 
→ **2 lone pairs on Xe**

5. O₃ (Ozone)

Central O has 6 valence electrons. It forms one single and one double bond (resonance). Bonds use 3 pairs = 6 electrons → 6 – 4 = 2 electrons = 1 lone pair. 
→ **1 lone pair on central O**

6. NH₃ (Ammonia)

Nitrogen has 5 valence electrons. Forms 3 bonds with H → uses 3 electrons. Remaining 2 electrons = 1 lone pair. 
→ **1 lone pair on N**

7. H₂O (Water)

Oxygen has 6 valence electrons. Forms 2 bonds with H → uses 2 electrons. Remaining 4 electrons = 2 lone pairs. 
→ **2 lone pairs on O**

Step 5: Count of Compounds with One Lone Pair

Compounds with exactly one lone pair on central atom: \[ \text{XeO}_3, \; \text{BrF}_5, \; \text{O}_3, \; \text{NH}_3 \] Total = **4**

Final Answer:

\[ \boxed{4} \]

Answer 2

To determine the number of compounds with one lone pair on the central atom, let’s examine each compound:

• O₃: Contains one lone pair on the central oxygen atom.
• H₂O: Contains two lone pairs on the central oxygen atom.
• SF₄: Contains one lone pair on the sulfur atom.
• ClF₃: Contains two lone pairs on the chlorine atom.
• NH₃: Contains one lone pair on the nitrogen atom.
• BrF₅: Contains one lone pair on the bromine atom.
• XeF₄: Contains two lone pairs on the xenon atom.

From the above, the compounds with exactly one lone pair on the central atom are: O₃, SF₄, NH₃, and BrF₅.

Total: 4 Compounds

So, the correct answer is: 4