HCI and HF are prepared by heating their salt `(NaCI` and `CaF_(2))` with conc. `H_(2)SO_(4)` but HI and HBr cannot he prepared by similar reaction because HBr and HI have

Options

A. Reducing properties
B. Oxidising property
C. Complex forming ability
D. None of these

Answer

To solve the question, we need to understand why HCl and HF can be prepared by heating their salts with concentrated H2SO4, while HI and HBr cannot.

### Step-by-Step Solution:

1. **Identify the salts used for preparation**:
- HCl is prepared from NaCl (sodium chloride).
- HF is prepared from CaF2 (calcium fluoride).
- HI is typically prepared from KI (potassium iodide).
- HBr is typically prepared from KBr (potassium bromide).

2. **Understand the reaction with concentrated H2SO4**:
- When NaCl is heated with concentrated H2SO4, the reaction is:
\[ \text{NaCl} + \text{H}_2\text{SO}_4 \rightarrow \text{Na}_2\text{SO}_4 + \text{HCl} \]
- When CaF2 is heated with concentrated H2SO4, the reaction is:
\[ \text{CaF}_2 + \text{H}_2\text{SO}_4 \rightarrow \text{CaSO}_4 + \text{HF} \]

3. **Examine the reactions for HI and HBr**:
- For HI, when KI is heated with concentrated H2SO4, the reaction is:
\[ \text{KI} + \text{H}_2\text{SO}_4 \rightarrow \text{I}_2 + \text{H}_2\text{S} + \text{Na}_2\text{SO}_4 + \text{H}_2\text{O} \]
Here, iodine (I2) is formed instead of HI.
- For HBr, when KBr is heated with concentrated H2SO4, the reaction is:
\[ \text{KBr} + \text{H}_2\text{SO}_4 \rightarrow \text{Br}_2 + \text{SO}_2 + \text{H}_2\text{O} \]
Here, bromine (Br2) is formed instead of HBr.

4. **Determine the reason for the difference**:
- HCl and HF do not have significant reducing properties, allowing them to be formed from their salts.
- However, HI and HBr have reducing properties, which means they can reduce H2SO4. In these reactions, H2SO4 acts as an oxidizing agent, leading to the formation of I2 and Br2 instead of HI and HBr.

5. **Conclusion**:
- The reason HI and HBr cannot be prepared in a similar manner as HCl and HF is because HBr and HI have reducing properties. Therefore, they cannot be formed from their salts when treated with concentrated H2SO4.

### Final Answer:
HBr and HI cannot be prepared by heating their salts with concentrated H2SO4 because HBr and HI have reducing properties.