Which of halogen acids indicated below is incorrect ?

Options

A. HF >HCI > HBr > HI ( acidic strength )
B. HI > HBr > HCI >HF ( reducing strength )
C. HI >HBr>HCI >HF (bond length)
D. HF >HCI >HBr >HI (thermal stability )

Answer

To determine which of the halogen acids is incorrect, we need to analyze the properties of the halogen acids: hydrogen fluoride (HF), hydrogen chloride (HCl), hydrogen bromide (HBr), and hydrogen iodide (HI).

### Step-by-Step Solution:

1. **Identify the Halogen Acids**:
The halogen acids we are considering are:
- Hydrogen fluoride (HF)
- Hydrogen chloride (HCl)
- Hydrogen bromide (HBr)
- Hydrogen iodide (HI)

2. **Understand the Bond Lengths**:
- The bond length increases as we move down the group from HF to HI. This is due to the increasing size of the halogen atoms.
- The order of bond lengths is:
- HF < HCl < HBr < HI

3. **Assess the Acidity**:
- The acidic strength of these acids is influenced by their bond lengths. A shorter bond length generally means a stronger bond, which makes it harder for the acid to release H+ ions.
- Therefore, the acidic strength order is:
- HI > HBr > HCl > HF
- This means HF is the weakest acid, while HI is the strongest.

4. **Evaluate Reducing Strength**:
- The reducing strength of these acids also follows the same order as their acidity. HI, having the weakest bond, can easily donate H+ ions, making it a strong reducing agent.

5. **Thermal Stability**:
- Thermal stability is inversely related to bond length. A longer bond length means lower thermal stability.
- Therefore, HI has the lowest thermal stability, while HF has the highest.

6. **Identify Incorrect Statement**:
- Based on the above analysis, if a statement claims that HF is stronger than HCl or HBr, or that HI is weaker than HF, it would be incorrect.
- The correct order of acidic strength is HF < HCl < HBr < HI, making any statement that contradicts this order incorrect.

### Conclusion:
The incorrect statement regarding the halogen acids is that HF is a stronger acid than HCl, which is not true.