Conc. `H_(2)SO_(4)`on addition to dry `KNO_(3)` gives brown fumes of :

Options

A. `SO_(2)`
B. `SO_(3)`
C. `SO`
D. `NO_(2)`

Explanation

To solve the question regarding the reaction between concentrated sulfuric acid (H₂SO₄) and dry potassium nitrate (KNO₃) that produces brown fumes, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reactants**:
- The reactants in this reaction are concentrated sulfuric acid (H₂SO₄) and potassium nitrate (KNO₃).

2. **Write the Initial Reaction**:
- When concentrated H₂SO₄ is added to KNO₃, a reaction occurs. The initial reaction can be represented as:
\[ \text{KNO}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{KHSO}_4 + \text{HNO}_3 \]
- Here, potassium hydrogen sulfate (KHSO₄) and nitric acid (HNO₃) are formed.

3. **Decomposition of Nitric Acid**:
- The nitric acid (HNO₃) produced can further decompose, especially under the influence of concentrated sulfuric acid, leading to the formation of nitrogen dioxide (NO₂), water (H₂O), and oxygen (O₂):
\[ 4 \text{HNO}_3 \rightarrow 2 \text{H}_2\text{O} + 4 \text{NO}_2 + \text{O}_2 \]

4. **Identify the Product**:
- The nitrogen dioxide (NO₂) produced in this reaction is a brown gas, which is responsible for the brown fumes observed.

5. **Conclusion**:
- Therefore, the brown fumes produced when concentrated sulfuric acid is added to dry potassium nitrate are due to nitrogen dioxide (NO₂).

### Final Answer:
The brown fumes are due to the formation of **NO₂** (nitrogen dioxide).

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