Strongest dipole - dipole interaction is present in the following substance

Options

A. Hydrogen chloride gas
B. Hydrogen fluoride gas
C. Water vapour
D. Ammonia gas

Answer

To determine which substance has the strongest dipole-dipole interaction among HCl, HF, H2O, and NH3, we can follow these steps:

### Step 1: Understand Dipole-Dipole Interactions
Dipole-dipole interactions occur between molecules that have permanent dipoles due to differences in electronegativity between the atoms involved. The greater the difference in electronegativity, the stronger the dipole-dipole interaction.

### Step 2: Determine Electronegativity Values
The electronegativity values for the relevant elements are:
- Fluorine (F): 4.0
- Oxygen (O): 3.5
- Nitrogen (N): 3.0
- Chlorine (Cl): 3.0
- Hydrogen (H): 2.1

### Step 3: Analyze Each Substance
1. **HCl**: The bond is between H (2.1) and Cl (3.0). The difference in electronegativity is 3.0 - 2.1 = 0.9.
2. **HF**: The bond is between H (2.1) and F (4.0). The difference in electronegativity is 4.0 - 2.1 = 1.9.
3. **H2O**: The bonds are between H (2.1) and O (3.5). The difference in electronegativity is 3.5 - 2.1 = 1.4.
4. **NH3**: The bonds are between H (2.1) and N (3.0). The difference in electronegativity is 3.0 - 2.1 = 0.9.

### Step 4: Compare the Differences
From the differences calculated:
- HCl: 0.9
- HF: 1.9
- H2O: 1.4
- NH3: 0.9

### Step 5: Identify the Strongest Interaction
The strongest dipole-dipole interaction will be in the substance with the largest electronegativity difference. Here, HF has the highest difference of 1.9, indicating that it has the strongest dipole-dipole interaction.

### Conclusion
Thus, the substance with the strongest dipole-dipole interaction is **HF (Hydrogen Fluoride)**.

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