Assertion : The reaction of ammonia solution with calomel is a disproportionation reaction in which a mixture Hg(II) amido chloride and mercury are formed
Reason : In a disproportionation reaction species under reaction is neither oxidised nor reduced.

Options

A. Both A and R are true and R is a correct explanation of A
B. Both A and R are true but R is not a correct explanation of A
C. A is true but R is false
D. Both A and R are false

Explanation

To solve the given question, we need to analyze both the assertion and the reason provided.

### Step 1: Understand the Assertion
The assertion states that the reaction of ammonia solution with calomel (Hg2Cl2) is a disproportionation reaction, resulting in the formation of Hg2 amido chloride and elemental mercury (Hg).

### Step 2: Write the Reaction
When ammonia (NH3) reacts with calomel (Hg2Cl2), the reaction can be represented as:
\[ \text{Hg}_2\text{Cl}_2 + 2 \text{NH}_3 \rightarrow \text{Hg}_2\text{(NH}_2\text{Cl)} + \text{Hg} + \text{NH}_4\text{Cl} \]

### Step 3: Determine the Oxidation States
- In calomel (Hg2Cl2), the oxidation state of mercury (Hg) can be calculated as follows:
\[ 2X - 2 = 0 \implies X = +1 \]
So, Hg in Hg2Cl2 has an oxidation state of +1.

- In Hg2 amido chloride (Hg2(NH2Cl)), one Hg is in the +2 oxidation state, while the other Hg is in the elemental state (0 oxidation state).

### Step 4: Identify Oxidation and Reduction
In the reaction:
- One Hg goes from +1 (in Hg2Cl2) to 0 (elemental Hg), which is a reduction.
- The other Hg goes from +1 to +2 (in Hg2 amido chloride), which is an oxidation.

### Step 5: Conclusion on the Assertion
Since the same species (Hg) is both oxidized and reduced in the reaction, this confirms that the reaction is indeed a disproportionation reaction. Therefore, the assertion is **true**.

### Step 6: Analyze the Reason
The reason states that in a disproportionation reaction, the species under reaction is neither oxidized nor reduced. This statement is **false** because, as we have established, in a disproportionation reaction, the same species is both oxidized and reduced.

### Final Conclusion
Thus, the assertion is true, and the reason is false. The correct answer is that the assertion is true, but the reason is false.

### Summary of the Solution
- The assertion is true: The reaction of ammonia with calomel is a disproportionation reaction.
- The reason is false: In a disproportionation reaction, the species is both oxidized and reduced.