The primary and secondary valencies of cobalt respectively in `[Co(NH_3)_5Cl]Cl_2` are:

Options

A. 3 and 5
B. 2 and 6
C. 2 and 8
D. 3 and 6

Answer

To determine the primary and secondary valencies of cobalt in the complex `[Co(NH₃)₅Cl]Cl₂`, we can follow these steps:

### Step 1: Identify the central metal atom and its ligands
- The central metal atom in the complex is cobalt (Co).
- The ligands attached to cobalt are five ammonia (NH₃) molecules and one chloride (Cl) ion.

### Step 2: Determine the primary valency (oxidation state)
- The primary valency corresponds to the oxidation state of the central metal atom.
- In the complex, ammonia (NH₃) is a neutral ligand, contributing zero to the oxidation state.
- The chloride ion (Cl) has a -1 charge, and since there are two chloride ions outside the coordination sphere, their total contribution is -2.

Let the oxidation state of cobalt be \( x \):
\[ x + (0 \times 5) + (-1) \times 1 + (-1) \times 2 = 0 \]
This simplifies to:
\[ x - 1 - 2 = 0 \]
\[ x - 3 = 0 \implies x = +3 \]
Thus, the primary valency of cobalt is +3.

### Step 3: Determine the secondary valency (coordination number)
- The secondary valency corresponds to the coordination number, which is the total number of ligands directly bonded to the central metal atom.
- In this complex, there are five ammonia ligands and one chloride ligand directly bonded to cobalt, giving a total of:
\[ 5 + 1 = 6 \]
Thus, the secondary valency of cobalt is 6.

### Conclusion
The primary and secondary valencies of cobalt in the complex `[Co(NH₃)₅Cl]Cl₂` are:
- Primary valency: +3
- Secondary valency: 6

### Final Answer
The primary and secondary valencies of cobalt respectively are **3 and 6**.

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