Which of the following statements is not true ?

Options

A. HOCl is a stronger acid than `HOBr`
B. HF is a stronger acid than HCl
C. Among halide ions, iodine is the most powerful reducing agent.
D. Fluorine is the only halogen that does not show a variable oxidation state

Explanation

To determine which of the following statements is not true, we will analyze each statement one by one.

### Step 1: Analyze Statement A
**Statement A:** HOCl is a stronger acid than HOBr.

- **Dissociation of HOCl:**
\[ HOCl \rightarrow OCl^- + H^+ \]
- **Dissociation of HOBr:**
\[ HOBr \rightarrow OBr^- + H^+ \]
- **Comparison of OCl^- and OBr^-:**
- Chlorine (Cl) is more electronegative than bromine (Br).
- The negative charge on the oxygen in OCl^- is stabilized more effectively due to the higher electronegativity of Cl compared to Br.
- **Conclusion:** HOCl is indeed a stronger acid than HOBr. This statement is true.

### Step 2: Analyze Statement B
**Statement B:** HF is a stronger acid than HCl.

- **Acidity Order of Hydrohalic Acids:**
- The order of acidity is: HI > HBr > HCl > HF.
- **Reasoning:**
- HF is less acidic than HCl because F^- is a very stable ion due to its high electronegativity, making HF less likely to dissociate into H^+ and F^-.
- **Conclusion:** This statement is false.

### Step 3: Analyze Statement C
**Statement C:** Among halide ions, iodine is the most powerful reducing agent.

- **Iodine's Behavior:**
- Iodine can easily lose electrons to form I^-, thus acting as a reducing agent.
- **Conclusion:** This statement is true.

### Step 4: Analyze Statement D
**Statement D:** Chlorine is the only halogen that does not show variable oxidation states.

- **Oxidation States of Halogens:**
- Chlorine can exhibit oxidation states of -1, +1, +3, +5, and +7.
- Other halogens (Br, I) also show variable oxidation states.
- **Conclusion:** This statement is false because chlorine does show variable oxidation states.

### Final Conclusion
The statement that is not true is **Statement B**: HF is a stronger acid than HCl.

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