Which one of the following statements is not true

Options

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

Answer

To determine which statement is not true among the given options, we will analyze each statement one by one.

### Step 1: Analyze the first statement
**Statement:** Among halides, iodine is the most powerful reducing agent.

**Analysis:**
- A reducing agent is a substance that donates electrons to another substance and gets oxidized in the process.
- Iodine (I2) is larger in size compared to other halogens, which makes it easier to lose electrons from its outermost shell.
- Therefore, iodine is indeed a powerful reducing agent.

**Conclusion:** This statement is **true**.

### Step 2: Analyze the second statement
**Statement:** Fluorine is the only halogen that does not show a variable oxidation state.

**Analysis:**
- Fluorine is in the second period of the periodic table and has no d-orbitals available for bonding.
- Due to its high electronegativity and lack of available orbitals, fluorine can only exhibit an oxidation state of -1.
- Other halogens, such as chlorine and bromine, can exhibit multiple oxidation states.

**Conclusion:** This statement is **true**.

### Step 3: Analyze the third statement
**Statement:** HOCl is a stronger acid than HOBr.

**Analysis:**
- To compare the acidic strength, we can look at the stability of their conjugate bases (ClO- and BrO-).
- Chlorine is more electronegative than bromine, which makes ClO- more stable than BrO-.
- A more stable conjugate base corresponds to a stronger acid. Therefore, HOCl is indeed a stronger acid than HOBr.

**Conclusion:** This statement is **true**.

### Step 4: Analyze the fourth statement
**Statement:** HF is a stronger acid than HCl.

**Analysis:**
- The bond strength between H and F is stronger than the bond strength between H and Cl due to the comparable sizes of H and F.
- Stronger bonds are harder to break, which means HF does not dissociate as easily in solution compared to HCl.
- Therefore, HCl is a stronger acid than HF because it dissociates more readily to release H+ ions.

**Conclusion:** This statement is **not true**.

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

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