`M("Salt")+"Dil. "HCl overset(Warm)to Pdarr+N uarr`
gas 'N' changes colour of `FeSO_(4)` solution into yellow solution then salt M in above reaction is

Options

A. `BaS_(2)O_(3)`
B. `Ag_(2)SO_(3)`
C. `AgNO_(2)`
D. `Pb(NO_(3))_(2)`

Explanation

To solve the question, we need to identify the salt M that, when reacted with dilute HCl and warmed, produces a gas N that changes the color of FeSO4 solution to yellow.

### Step-by-Step Solution:

1. **Identify the Reaction**: The question states that salt M reacts with dilute HCl when warmed to produce two products: a salt (P) and a gas (N). The gas N is crucial because it changes the color of FeSO4 solution.

2. **Analyze the Options**: We have four options for salt M:
- A) BaS2O3
- B) Ag2SO3
- C) AgNO2
- D) Pb(NO3)2

3. **Test Each Option**:
- **Option A: BaS2O3**
- Reaction: BaS2O3 + HCl → BaCl2 + SO2 (gas)
- Result: SO2 does not change the color of FeSO4 solution. It remains green.

- **Option B: Ag2SO3**
- Reaction: Ag2SO3 + HCl → AgCl (precipitate) + SO2 (gas)
- Result: SO2 does not change the color of FeSO4 solution. It remains green.

- **Option C: AgNO2**
- Reaction: AgNO2 + HCl → AgCl (precipitate) + NO2 (gas)
- Result: NO2 reacts with FeSO4, changing Fe2+ to Fe3+, resulting in a yellow solution.

- **Option D: Pb(NO3)2**
- Reaction: Pb(NO3)2 + HCl → No significant reaction.
- Result: No change in color of FeSO4 solution.

4. **Conclusion**: The only option that produces a gas (N) that changes the color of FeSO4 solution to yellow is **C) AgNO2**. Therefore, the salt M in the reaction is AgNO2.

### Final Answer:
The salt M in the above reaction is **AgNO2**.