Which of the following statements is true about hydrogen bonding?

Options

A. Cl and N have comparable electronegativities yet there is no H - bonding in HCl because size of Cl is large
B. Intermolecular H - bonding results in decrease in m.p and b.p.
C. lce has maximum density at `0^@C` due to H - bonding
D. `KHCl_2 (HCl_2^(-))` exists but `KHF_2(HF_2^(-))` does not exist due to lack of H - bonding in HCl

Answer

To determine which statement about hydrogen bonding is true, let's analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding Hydrogen Bonding**:
- Hydrogen bonding occurs when hydrogen is covalently bonded to a highly electronegative atom (like F, O, or N) and experiences an attraction to another electronegative atom. This is a type of dipole-dipole interaction.

2. **Analyzing Option 1**:
- The statement claims that chlorine and hydrogen have comparable electronegativities, yet there is no hydrogen bonding in HCl due to the size of chlorine.
- **Evaluation**: While chlorine is indeed electronegative, the bond in HCl is a strong covalent bond rather than a hydrogen bond. The large size of chlorine prevents effective hydrogen bonding.
- **Conclusion**: This statement is true.

3. **Analyzing Option 2**:
- The statement claims that intermolecular hydrogen bonding results in a decrease in melting point and boiling point.
- **Evaluation**: This is incorrect. Intermolecular hydrogen bonding typically increases the melting and boiling points of substances due to stronger intermolecular forces.
- **Conclusion**: This statement is false.

4. **Analyzing Option 3**:
- The statement claims that ice has maximum density at zero degrees centigrade due to hydrogen bonding.
- **Evaluation**: Ice is actually less dense than liquid water due to the hydrogen bonding arrangement, which forms a lattice structure. Therefore, this statement is false.
- **Conclusion**: This statement is false.

5. **Analyzing Option 4**:
- The statement claims that HCl2 exists but HF2 does not exist due to the lack of hydrogen bonding in HCl.
- **Evaluation**: HCl2 does not exist as a stable species, while HF2- does exist because of the strong hydrogen bonding between H and F. Hence, this statement is also false.
- **Conclusion**: This statement is false.

### Final Conclusion:
The only true statement regarding hydrogen bonding from the options provided is **Option 1**.

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