Assertion : Fluorine oxidises water to oxygen whereas chlorine and bromine react with water to form corresponding hydrohalic and hypohalous acids.
Reason : The reactivity of halogens increases down the group.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion is true but reason is false.
D. If both assertion and reason are false.

Explanation

To analyze the given assertion and reason, let's break down the information step by step.

**Step 1: Understand the Assertion**
- The assertion states that fluorine oxidizes water to produce oxygen, while chlorine and bromine react with water to form hydrohalic acids (HCl, HBr) and hypohalous acids (HOCl, HOBr).
- This is true. Fluorine is a strong oxidizing agent and can oxidize water to produce oxygen gas.

**Step 2: Analyze the Reactions**
- For fluorine:
\[ 2 \text{H}_2\text{O} + 2 \text{F}_2 \rightarrow 4 \text{HF} + \text{O}_2 \]
- For chlorine:
\[ \text{Cl}_2 + 2 \text{H}_2\text{O} \rightarrow 2 \text{HCl} + \text{HOCl} \]
- For bromine:
\[ \text{Br}_2 + 2 \text{H}_2\text{O} \rightarrow 2 \text{HBr} + \text{HOBr} \]
- These reactions confirm the assertion.

**Step 3: Understand the Reason**
- The reason states that the reactivity of halogens increases down the group.
- This is false. In fact, the reactivity of halogens decreases down the group. As you move from fluorine to iodine, the size of the atoms increases, and the ability to attract electrons decreases.

**Step 4: Conclusion**
- The assertion is true: fluorine oxidizes water to oxygen, while chlorine and bromine react with water to form acids.
- The reason is false: the reactivity of halogens does not increase down the group; it actually decreases.
- Therefore, the correct answer is that the assertion is true, but the reason is false.

### Summary
- **Assertion**: True
- **Reason**: False
- **Conclusion**: Assertion true, reason false.