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 of the statements regarding hydrogen bonding is true, we will analyze each option one by one.

### Step-by-Step Solution:

1. **Understanding Hydrogen Bonding**:
Hydrogen bonding occurs when a hydrogen atom covalently bonded to a highly electronegative atom (like N, O, or F) interacts with another electronegative atom. The size and electronegativity of the atoms involved are crucial for the formation of hydrogen bonds.

2. **Evaluating Option 1**:
- Statement: "Chlorine and nitrogen have comparable electronegativities, yet there is no hydrogen bonding in HCl because the size of chlorine is larger."
- Analysis: Chlorine (Cl) is indeed larger than nitrogen (N), and while both have comparable electronegativities, the larger size of Cl reduces the effectiveness of hydrogen bonding. Therefore, this statement is true.

3. **Evaluating Option 2**:
- Statement: "Intermolecular hydrogen bonding results in a decrease in melting and boiling points."
- Analysis: Intermolecular hydrogen bonding typically increases the melting and boiling points of substances (like water and alcohols) due to stronger interactions between molecules. Hence, this statement is false.

4. **Evaluating Option 3**:
- Statement: "Ice has maximum density at 0 degrees Celsius."
- Analysis: Ice actually has its maximum density at 4 degrees Celsius. Below this temperature, ice expands due to the hydrogen bonding structure. Therefore, this statement is false.

5. **Evaluating Option 4**:
- Statement: "KHCl2 exists but KHF2 doesn't exist due to lack of hydrogen bonding in HCl."
- Analysis: KHF2 does exist due to the strong hydrogen bonding in HF. However, KHCl2 is not stable. Thus, this statement is also false.

### Conclusion:
After analyzing all the options, we find that **Option 1** is the only true statement regarding hydrogen bonding.

### Final Answer:
**Option 1 is the true statement about hydrogen bonding.**

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