A mixture when heated with dil `H_(2)SO_(4)` does not evolve brown vapours but when heated with conc `H_(2)SO_(4)`, brown vapours are obtained. with `AgNO_(3)` soin do not give any precipitate .The mixture contain

Options

A. `NO_(2)^(Theta)`
B. `NO_(3)^(Theta)`
C. `I^(Theta)`
D. `Br^(Theta)`

Answer

To solve the problem step by step, we need to analyze the given information about the mixture and the reactions involved.

### Step 1: Analyze the behavior with dilute H₂SO₄
- The mixture does not evolve brown vapors when heated with dilute H₂SO₄. This indicates that the anions present in the mixture do not produce brown gases under these conditions.

**Hint:** Consider what types of anions typically do not react with dilute sulfuric acid to produce brown gases.

### Step 2: Analyze the behavior with concentrated H₂SO₄
- When heated with concentrated H₂SO₄, brown vapors are obtained. This suggests that the anion present in the mixture must be capable of producing brown gases (like NO₂) when reacted with concentrated sulfuric acid.

**Hint:** Think about which anions can react with concentrated sulfuric acid to produce brown gases.

### Step 3: Consider the reaction with AgNO₃
- The mixture does not give any precipitate with AgNO₃. This is crucial because certain anions (like I⁻ and Br⁻) would form precipitates (AgI and AgBr) when reacted with silver nitrate.

**Hint:** Recall which anions typically form precipitates with AgNO₃ and eliminate them from consideration.

### Step 4: Identify the possible anions
- Since the mixture does not give a precipitate with AgNO₃, we can eliminate I⁻ and Br⁻ from our list of possible anions.
- The only anion that fits the criteria of producing brown vapors when reacted with concentrated H₂SO₄ and not forming a precipitate with AgNO₃ is the nitrate ion (NO₃⁻).

**Hint:** Check the reactions of other common anions with concentrated H₂SO₄ to see if they produce brown gases.

### Step 5: Conclusion
- Based on the analysis, the anion present in the mixture is nitrate (NO₃⁻).

**Final Answer:** The mixture contains the nitrate ion (NO₃⁻).