Which of the following substances has the least covalent character ?

Options

A. `Cl_(2)O`
B. `NCl_(3)`
C. `PbCl_(2)`
D. `BaCl_(2)`

Explanation

To determine which of the given substances has the least covalent character, we can apply Fajan's rule, which states that the covalent character of an ionic compound is influenced by the size and charge of the cations and anions involved.

### Step-by-Step Solution:

1. **Identify the Substances**:
Let's assume the substances given are:
- A) BaCl2
- B) Cl2O
- C) PbCl2
- D) NCl3

2. **Identify Cations and Anions**:
- For BaCl2: Cation = Ba²⁺, Anion = Cl⁻
- For Cl2O: Cation = Cl⁺, Anion = O²⁻
- For PbCl2: Cation = Pb²⁺, Anion = Cl⁻
- For NCl3: Cation = N³⁺, Anion = Cl⁻

3. **Apply Fajan's Rule**:
According to Fajan's rule:
- Covalent character is directly proportional to the size of the anion.
- Covalent character is inversely proportional to the size of the cation.
- Covalent character is directly proportional to the charge of both cation and anion.

4. **Analyze the Cations**:
- **Ba²⁺**: Group 2, Period 6 (larger size)
- **Pb²⁺**: Group 14, Period 6 (smaller than Ba²⁺)
- **Cl⁺**: Period 3 (smaller than Ba²⁺ and Pb²⁺)
- **N³⁺**: Period 2 (smallest size)

Larger cations (Ba²⁺ and Pb²⁺) will have less covalent character compared to smaller cations (Cl⁺ and N³⁺).

5. **Analyze the Anions**:
- **Cl⁻**: Smaller size, single negative charge.
- **O²⁻**: Larger size, double negative charge (more covalent character).

6. **Comparison of Covalent Character**:
- Between BaCl2 and Cl2O:
- Ba²⁺ is larger than Cl⁺, thus BaCl2 has less covalent character.
- O²⁻ has more charge and size than Cl⁻, thus Cl2O has more covalent character.
- Between PbCl2 and BaCl2:
- Pb²⁺ is smaller than Ba²⁺, thus PbCl2 has more covalent character than BaCl2.
- Between NCl3 and the others:
- N³⁺ is significantly smaller than Ba²⁺, Pb²⁺, and Cl⁺, leading to a higher covalent character.

7. **Conclusion**:
After comparing all the substances, BaCl2 has the least covalent character due to its larger cation (Ba²⁺) and smaller charge on the anion (Cl⁻).

### Final Answer:
**BaCl2** has the least covalent character.