Which halogen liberates oxygen, when passed through hot concentrated KOH solution ?

Answer

To determine which halogen liberates oxygen when passed through hot concentrated KOH solution, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reaction Conditions**: We are dealing with hot concentrated KOH solution. KOH is a strong base and can react with halogens.

2. **Consider the Halogens**: The halogens include fluorine (F2), chlorine (Cl2), bromine (Br2), and iodine (I2). We need to evaluate which of these can liberate oxygen when reacted with hot concentrated KOH.

3. **Analyze the Reaction with Fluorine**:
- When fluorine gas (F2) is passed through hot concentrated KOH, it reacts to form potassium fluoride (KF) and liberates oxygen gas (O2).
- The balanced chemical equation for this reaction is:
\[ 4 \text{KOH} + \text{F}_2 \rightarrow 4 \text{KF} + 2 \text{H}_2\text{O} + \text{O}_2 \]
- From this equation, we can see that oxygen is indeed liberated.

4. **Check Other Halogens**:
- Chlorine (Cl2) can also react with KOH but does not liberate oxygen in the same manner.
- Bromine (Br2) and iodine (I2) do not liberate oxygen when reacted with hot concentrated KOH.

5. **Conclusion**: Based on the analysis, the halogen that liberates oxygen when passed through hot concentrated KOH solution is **Fluorine (F2)**.

### Final Answer:
The halogen that liberates oxygen when passed through hot concentrated KOH solution is **Fluorine (F2)**.