Pick out the incorrect statement regarding halogens

Options

A. Chlorine is hydrolysed by water to form hydrochloric acid and hypochlorous acid
B. Bromine and iodine react with NaOH solution to form halide and halate ion
C. Chlorine reacts with cold dilute `NaOH` solution to give sodium chloride and sodium chlorate
D. Iodine forms a deep blue colour with starch solution

Answer

To determine the incorrect statement regarding halogens, let's analyze each option provided in the question step by step.

### Step 1: Analyze the first statement
**Statement 1:** Chlorine is hydrolyzed by water to form hydrochloric acid and hypochlorous acid.

- Reaction:
\[ \text{Cl}_2 + \text{H}_2\text{O} \rightleftharpoons \text{HOCl} + \text{HCl} \]
- This reaction indicates that chlorine reacts with water to produce hydrochloric acid (HCl) and hypochlorous acid (HOCl).
- **Conclusion:** This statement is correct.

**Hint:** Check if the reaction products match the statement.

### Step 2: Analyze the second statement
**Statement 2:** Bromine and iodine react with sodium hydroxide solution to form halide and halate ions.

- Reaction for bromine:
\[ \text{Br}_2 + 2 \text{NaOH} \rightarrow \text{NaBr} + \text{NaBrO}_3 + \text{H}_2\text{O} \]
- Reaction for iodine:
\[ \text{I}_2 + 6 \text{NaOH} \rightarrow 5 \text{NaI} + \text{NaIO}_3 + 3 \text{H}_2\text{O} \]
- Both reactions show that bromine and iodine react with sodium hydroxide to produce halide ions (NaBr, NaI) and halate ions (NaBrO3, NaIO3).
- **Conclusion:** This statement is correct.

**Hint:** Confirm that both halide and halate ions are produced in the reactions.

### Step 3: Analyze the third statement
**Statement 3:** Chlorine reacts with cold dilute sodium hydroxide solution to give sodium chloride and sodium hypochlorite.

- Reaction:
\[ \text{Cl}_2 + 2 \text{NaOH} \rightarrow \text{NaCl} + \text{NaOCl} + \text{H}_2\text{O} \]
- This reaction indicates that chlorine reacts with cold dilute sodium hydroxide to produce sodium chloride (NaCl) and sodium hypochlorite (NaOCl).
- **Conclusion:** This statement is incorrect because it implies that sodium hypochlorite is the only product, while it also produces sodium chloride and water.

**Hint:** Verify the products of the reaction to see if they match the statement.

### Step 4: Analyze the fourth statement
**Statement 4:** Iodine forms a deep blue color with starch solution.

- Reaction:
\[ \text{KI} + \text{NO}_2 \rightarrow \text{KNO}_2 + \text{I}_2 \]
- The free iodine (I2) reacts with starch to form a blue complex, which is a well-known test for iodine.
- **Conclusion:** This statement is correct.

**Hint:** Recall the classic iodine-starch test for color change.

### Final Conclusion
After analyzing all the statements, the incorrect statement regarding halogens is:

**Option 3:** Chlorine reacts with cold dilute sodium hydroxide solution to give sodium chloride and sodium hypochlorite.

This statement is misleading as it does not account for the water produced in the reaction and implies a different stoichiometry.