Consider the following reactions and answer the following questions.
M(Double salt)+`NH_(4)Cl(s)+NH_(4)OH to `No ppt.
M(double salt)+`NaOH` solution`toN uarr+Pdarr` (coloured ppt.)
Q. Reaction does not occur with salt M and gas N:

Options

A. `NaNO_(2)+dil.H_(2)SO_(4)+M("salt solution")to`
B. `HgI_(2)+Nuarr to `
C. M(salt solution) `+H_(2)S to `
D. M (salt solution)`+Br_(2)to`

Answer

To solve the question, we need to analyze the given reactions involving the double salt M, which is identified as Mohr's salt (FeSO4·(NH4)2SO4·6H2O). We will determine which of the provided options does not react with salt M and gas N (which is ammonia, NH3).

### Step-by-Step Solution:

1. **Identify the Double Salt (M)**:
- The double salt M is Mohr's salt, which has the formula FeSO4·(NH4)2SO4·6H2O. It contains ferrous ions (Fe²⁺) and ammonium ions (NH4⁺).

2. **Analyze the First Reaction**:
- The first reaction is:
\[ \text{M (double salt)} + \text{NH}_4\text{Cl (s)} + \text{NH}_4\text{OH} \rightarrow \text{No precipitate} \]
- This indicates that the combination of Mohr's salt with ammonium chloride and ammonium hydroxide does not produce any precipitate.

3. **Analyze the Second Reaction**:
- The second reaction is:
\[ \text{M (double salt)} + \text{NaOH solution} \rightarrow \text{N (gas)} + \text{P (colored precipitate)} \]
- Here, the NaOH reacts with the double salt to release ammonia gas (N) and forms a precipitate of ferrous hydroxide (Fe(OH)₂), which is colored (green).

4. **Identify the Gas (N)**:
- From the second reaction, we identify that gas N is ammonia (NH3).

5. **Evaluate the Options**:
- We need to check which of the given reactions does not occur with salt M (Mohr's salt) and gas N (ammonia).
- The options provided are:
1. NaNO2 + dilute H2SO4 + Mohr's salt → Brown ring complex (reaction occurs)
2. HgI2 + NH3 + H2O → Brown precipitate (reaction occurs)
3. Mohr's salt + H2S (gas) → No reaction (this is the option we are looking for)
4. Mohr's salt + Br2 → Yellow solution (reaction occurs)

6. **Conclusion**:
- The only reaction that does not occur with salt M and gas N (ammonia) is the third option, which involves H2S gas. Therefore, the answer is option 3.

### Final Answer:
The reaction that does not occur with salt M and gas N is option 3 (Mohr's salt + H2S gas).