Addition of one drop of `HNO_(3)` in group (III) analysis is to (a) _____.

Answer

To answer the question regarding the addition of one drop of HNO₃ in group (III) analysis, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Group Analysis**:
- In qualitative inorganic analysis, substances are categorized into groups based on their chemical properties. Group III typically includes cations such as Fe²⁺, Al³⁺, and Cr³⁺.

2. **Role of Nitric Acid (HNO₃)**:
- Nitric acid is a strong oxidizing agent. Its addition is crucial in the analysis of certain metal ions.

3. **Oxidation Reaction**:
- When HNO₃ is added to a solution containing ferrous ions (Fe²⁺), it oxidizes these ions to ferric ions (Fe³⁺). This is important for the identification of iron in the analysis.

4. **Example Reaction**:
- The reaction can be represented as follows:
\[ 3 \text{FeSO}_4 + 4 \text{HNO}_3 \rightarrow 3 \text{Fe}_2(SO_4)_3 + 4 \text{NO} + 2 \text{H}_2\text{O} \]
- In this reaction, ferrous sulfate reacts with nitric acid to produce ferric sulfate, nitrogen monoxide (NO), and water.

5. **Conclusion**:
- Therefore, the addition of one drop of HNO₃ in group (III) analysis is to **oxidize Fe²⁺ ions to Fe³⁺ ions**.

### Final Answer:
The addition of one drop of HNO₃ in group (III) analysis is to **oxidize Fe²⁺ to Fe³⁺ ions**.

---