The primary valency of the metal ion in the co-ordination compound, `K_2[Ni(CN)_4]` is

Options

A. Four
B. Zero
C. Two
D. Six

Answer

To determine the primary valency of the metal ion in the coordination compound \( K_2[Ni(CN)_4] \), we can follow these steps:

### Step 1: Identify the coordination compound
The given coordination compound is \( K_2[Ni(CN)_4] \). Here, \( Ni \) is the central metal ion surrounded by four cyanide ions (\( CN^- \)).

**Hint**: Look for the central metal ion and the ligands attached to it in the coordination compound.

### Step 2: Understand the concept of primary and secondary valency
- **Primary valency** refers to the charge on the metal ion that is satisfied by counter ions (in this case, the potassium ions \( K^+ \)).
- **Secondary valency** refers to the number of coordinate bonds formed by the metal ion with the ligands.

**Hint**: Remember that primary valency is related to the overall charge balance of the compound.

### Step 3: Determine the charge of the metal ion
In \( K_2[Ni(CN)_4] \):
- The compound is neutral overall.
- Each potassium ion \( K^+ \) contributes a charge of +1. Since there are 2 potassium ions, they contribute a total of +2 charge.
- The cyanide ion \( CN^- \) has a charge of -1, and there are 4 cyanide ions, contributing a total of -4 charge.

Now, let’s set up the charge balance:
\[ \text{Charge from K} + \text{Charge from Ni} + \text{Charge from CN} = 0 \]
\[ +2 + \text{Charge of Ni} - 4 = 0 \]

Solving for the charge of Ni:
\[ \text{Charge of Ni} = +4 - 2 = +2 \]

**Hint**: Calculate the total charge from the ligands and counter ions to find the charge on the metal ion.

### Step 4: Identify the primary valency
Since the charge on the nickel ion \( Ni \) is +2, this indicates that the primary valency of the metal ion is satisfied by the 2 potassium ions \( K^+ \).

**Hint**: The primary valency is equal to the charge on the metal ion that is balanced by the counter ions.

### Conclusion
The primary valency of the metal ion in the coordination compound \( K_2[Ni(CN)_4] \) is **2**.

**Final Answer**: 2