Which of the following has primary valeny `2""?

Options

A. `[Co(NH_(3))_(5)CI]CI`
B. `[Co(NH_(3))_(4)CI_(2)]CI`
C. `[Co(NH_(3))_(3)CI_(3)]`
D. `[Co(H_(2)O)_(4)CI_(2)]CI`

Answer

To determine which of the given compounds has a primary valency of 2, we need to analyze the oxidation states of the metal in each compound. The primary valency corresponds to the oxidation state of the metal ion.

### Step-by-Step Solution:

1. **Identify the Compounds**: The compounds given are:
- A: [Co(NH3)4Cl2]Cl
- B: [Co(NH3)3Cl3]
- C: [Co(NH3)5Cl]Cl2
- D: [Co(H2O)2Cl2]

2. **Assign Oxidation States**:
- For each compound, we will assign oxidation states to the metal (Co) and calculate the overall charge.

3. **Compound A: [Co(NH3)4Cl2]Cl**:
- Let the oxidation state of Co be \( x \).
- NH3 is neutral, and Cl has a charge of -1.
- The equation becomes:
\[ x + 4(0) + 2(-1) + (-1) = 0 \]
\[ x - 2 - 1 = 0 \implies x = +3 \]
- **Primary valency = +3**.

4. **Compound B: [Co(NH3)3Cl3]**:
- Let the oxidation state of Co be \( x \).
- The equation becomes:
\[ x + 3(0) + 3(-1) = 0 \]
\[ x - 3 = 0 \implies x = +3 \]
- **Primary valency = +3**.

5. **Compound C: [Co(NH3)5Cl]Cl2**:
- Let the oxidation state of Co be \( x \).
- The equation becomes:
\[ x + 5(0) + (-1) + 2(-1) = 0 \]
\[ x - 1 - 2 = 0 \implies x = +3 \]
- **Primary valency = +3**.

6. **Compound D: [Co(H2O)2Cl2]**:
- Let the oxidation state of Co be \( x \).
- The equation becomes:
\[ x + 2(0) + 2(-1) = 0 \]
\[ x - 2 = 0 \implies x = +2 \]
- **Primary valency = +2**.

### Conclusion:
The compound that has a primary valency of 2 is **D: [Co(H2O)2Cl2]**.