Given the molecular formula of the hexacoordinated complexes (A) `[CoCl_(3).6NH_3]` (B) `[CoCl_(3).5NH_3]` (C) `CoCl_(3).4NH_3`. If the number of coordinated `NH_3` molecules in A, B and C respectively are 6, 5 and 4, the primary valency in (A), (B) and (C) are:

Options

A. (a) 6, 5, 4
B. (b) 3, 2, 1
C. (c) 0, 1, 2
D. (d) 3, 3, 3

Explanation

To determine the primary valency of the hexacoordinated complexes (A), (B), and (C), we need to analyze the given molecular formulas and their coordination with NH₃ and Cl⁻ ions.

### Step-by-step Solution:

1. **Understanding the Coordination Complexes**:
- The complexes are:
- (A) \[CoCl_3 \cdot 6NH_3\]
- (B) \[CoCl_3 \cdot 5NH_3\]
- (C) \[CoCl_3 \cdot 4NH_3\]
- Each complex has a central cobalt ion (Co) surrounded by ligands (NH₃ and Cl⁻).

2. **Identifying the Coordination Number**:
- The coordination number is the total number of ligand attachments to the central metal ion. In all three complexes, the coordination number is 6 (as indicated by the presence of 6 ligands in total).

3. **Determining the Primary Valency**:
- The primary valency is related to the ionizable part of the complex, which is satisfied by negative charges (anions).
- In these complexes, Cl⁻ ions are the ionizable components.

4. **Analyzing Each Complex**:
- **For Complex (A)**:
- \[CoCl_3 \cdot 6NH_3\]
- There are 3 Cl⁻ ions. Therefore, the primary valency is 3.

- **For Complex (B)**:
- \[CoCl_3 \cdot 5NH_3\]
- There are still 3 Cl⁻ ions, but since there are only 5 NH₃, 1 Cl⁻ is ionizable. Thus, the primary valency is also 3.

- **For Complex (C)**:
- \[CoCl_3 \cdot 4NH_3\]
- Again, there are 3 Cl⁻ ions, but with only 4 NH₃, 2 Cl⁻ are ionizable. Thus, the primary valency is 3.

5. **Final Summary of Primary Valencies**:
- For (A): Primary valency = 3
- For (B): Primary valency = 3
- For (C): Primary valency = 3

### Final Answer:
- The primary valencies for complexes (A), (B), and (C) are all 3.