Which of the following reacts most slowly with nitric acid.

Options

A. Phosphorus
B. Chlorine
C. Sulphur
D. Iodine

Answer

To determine which of the following substances reacts most slowly with nitric acid (HNO3), we need to analyze the reactions of HNO3 with various elements or compounds.

1. **Understanding Nitric Acid as an Oxidizing Agent**:
- Nitric acid contains nitrogen in the +5 oxidation state, making it a strong oxidizing agent. It can oxidize various substances, but the rate of reaction can vary significantly depending on the substance involved.

2. **Reactions with Different Elements**:
- **Phosphorus (P)**:
- When phosphorus reacts with nitric acid, it forms phosphoric acid (H3PO4) and nitrogen dioxide (NO2). The reaction can be represented as:
\[ 2P + 10HNO3 \rightarrow 2H3PO4 + 10NO2 + 2H2O \]
- This reaction occurs at a moderate rate.

- **Sulfur (S)**:
- Sulfur reacts with nitric acid to produce sulfuric acid (H2SO4) and nitrogen dioxide (NO2):
\[ S + 6HNO3 \rightarrow H2SO4 + 6NO2 + 2H2O \]
- This reaction is relatively vigorous.

- **Iodine (I)**:
- Iodine reacts with nitric acid to form periodic acid (HIO3) and nitrogen dioxide (NO2):
\[ I2 + 10HNO3 \rightarrow 2HIO3 + 10NO2 + 4H2O \]
- This reaction also occurs vigorously.

- **Chlorine (Cl)**:
- Chlorine reacts with nitric acid but does so very slowly compared to the other substances. The reaction can be represented as:
\[ Cl2 + 6HNO3 \rightarrow 2HClO3 + 6NO2 + 2H2O \]
- Chlorine is also an oxidizing agent, which contributes to the slow reaction rate with nitric acid.

3. **Conclusion**:
- Among phosphorus, sulfur, iodine, and chlorine, chlorine reacts most slowly with nitric acid. Therefore, the correct answer to the question is **Chlorine (Cl)**.

### Summary:
The substance that reacts most slowly with nitric acid is **Chlorine (Cl)**.