Pick out incorrect statement about `K_(2)Cr_(2)O_(7)`

Options

A. It oxidizes acidified solution of `H_(2)S` to S
B. It oxidizes KI to `I_(2)`
C. It oxidizes HCl to `Cl_(2)`
D. It gives oxygen, which treated with cold dil. `H_(2)SO_(4)`

Answer

To determine the incorrect statement about \( K_2Cr_2O_7 \) (potassium dichromate), let's analyze each statement step by step.

### Step-by-Step Solution:

1. **Statement A: It oxidizes acidic solution of \( H_2S \) to \( S \).**
- **Analysis:**
- In acidic medium, \( K_2Cr_2O_7 \) acts as a strong oxidizing agent.
- The reaction can be represented as:
\[ K_2Cr_2O_7 + 3H_2S + 4H_2SO_4 \rightarrow K_2SO_4 + Cr_2(SO_4)_3 + 3S + 7H_2O \]
- Here, sulfur in \( H_2S \) is oxidized from -2 to 0 (elemental sulfur), and chromium is reduced from +6 to +3.
- **Conclusion:** This statement is **correct**.

2. **Statement B: It oxidizes \( KI \) to \( I_2 \).**
- **Analysis:**
- In acidic medium, \( K_2Cr_2O_7 \) can oxidize potassium iodide to iodine.
- The reaction can be represented as:
\[ K_2Cr_2O_7 + 6KI + 7H_2SO_4 \rightarrow 4K_2SO_4 + 2Cr_2(SO_4)_3 + 3I_2 + 7H_2O \]
- Here, iodine is oxidized from -1 (in \( KI \)) to 0 (elemental iodine), and chromium is reduced from +6 to +3.
- **Conclusion:** This statement is **correct**.

3. **Statement C: It oxidizes \( HCl \) to \( Cl_2 \).**
- **Analysis:**
- \( K_2Cr_2O_7 \) can oxidize hydrochloric acid to chlorine gas.
- The reaction can be represented as:
\[ K_2Cr_2O_7 + 6HCl \rightarrow 2CrCl_3 + 3Cl_2 + 2KCl + 7H_2O \]
- Here, chlorine is oxidized from -1 (in \( HCl \)) to 0 (elemental chlorine), and chromium is reduced from +6 to +3.
- **Conclusion:** This statement is **correct**.

4. **Statement D: It gives oxygen when treated with cold dilute \( H_2SO_4 \).**
- **Analysis:**
- When \( K_2Cr_2O_7 \) is treated with cold dilute sulfuric acid, it does not produce oxygen.
- The reaction can be represented as:
\[ K_2Cr_2O_7 + 2H_2SO_4 \rightarrow 2CrO_3 + 2KHSO_4 + H_2O \]
- There is no formation of oxygen in this reaction.
- **Conclusion:** This statement is **incorrect**.

### Final Answer:
The incorrect statement about \( K_2Cr_2O_7 \) is **Statement D**.

---