In which of the following reactions a brown coloured gas is evolved ?

Options

A. `KBr (s) + " dil." H_(2)SO_(4) to`
B. `NH_(4)NO_(2) overset(Delta)to`
C. `NaNO_(3) underset(800^(@)C) overset(Delta)to`
D. `AgNO_(3)(s)+conc. H_(2)SO_(4) to`

Answer

To determine in which of the given reactions a brown-colored gas is evolved, we will analyze each reaction step by step.

### Step 1: Analyze the first reaction
**Reaction:** Potassium bromate (KBr) + Dilute sulfuric acid (H2SO4)

**Products:** The reaction produces sulfur dioxide (SO2), potassium sulfate (K2SO4), water (H2O), and bromine gas (Br2).

**Observation:** Bromine gas (Br2) is brown in color. Therefore, this reaction evolves a brown-colored gas.

### Step 2: Analyze the second reaction
**Reaction:** Ammonium nitrite (NH4NO2)

**Condition:** When heated, ammonium nitrite decomposes.

**Products:** This decomposition produces colorless nitrogen gas (N2) and water vapor (H2O).

**Observation:** No brown-colored gas is evolved in this reaction.

### Step 3: Analyze the third reaction
**Reaction:** Sodium nitrate (NaNO3)

**Condition:** Upon heating to 800 degrees Celsius.

**Products:** The decomposition results in sodium nitrite (NaNO2) and colorless oxygen gas (O2).

**Observation:** No brown-colored gas is evolved in this reaction.

### Step 4: Analyze the fourth reaction
**Reaction:** Silver nitrate (AgNO3) + Concentrated sulfuric acid (H2SO4)

**Products:** This reaction produces nitric acid (HNO3) and silver sulfate (Ag2SO4).

**Observation:** No gas is evolved in this reaction.

### Conclusion
After analyzing all the reactions, we find that only the first reaction (KBr + H2SO4) evolves a brown-colored gas (Br2). Therefore, the correct option is:

**Correct Option:** Reaction A (KBr + H2SO4)

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