Which of the following gas is expected to have highest value of Van der Waal's constant 'a'

Options

A. `NH_3`
B. `H_2`
C. `N_2`
D. `He`

Answer

To determine which gas is expected to have the highest value of Van der Waals constant 'a', we need to analyze the intermolecular forces of attraction present in the given gases. The Van der Waals constant 'a' is directly related to the strength of these intermolecular forces; the stronger the forces, the higher the value of 'a'.

### Step-by-Step Solution:

1. **Understand Van der Waals Constant 'a':**
- The Van der Waals constant 'a' represents the magnitude of attractive forces between gas molecules. A higher value of 'a' indicates stronger intermolecular forces.

2. **Identify the Gases:**
- The question provides a list of gases (let's assume they include ammonia (NH₃), hydrogen (H₂), nitrogen (N₂), and helium (He)).

3. **Analyze Intermolecular Forces:**
- **Ammonia (NH₃):**
- Ammonia has hydrogen bonding due to the presence of a highly electronegative nitrogen atom and hydrogen atoms. Each ammonia molecule can form multiple hydrogen bonds (up to 4), leading to strong intermolecular attractions.
- **Hydrogen (H₂):**
- Hydrogen is a non-polar molecule with only London dispersion forces, which are relatively weak.
- **Nitrogen (N₂):**
- Nitrogen is also a non-polar molecule with London dispersion forces, similar to hydrogen, and thus has weak intermolecular attractions.
- **Helium (He):**
- Helium is a noble gas and is non-polar, exhibiting only London dispersion forces, which are the weakest among the forces discussed.

4. **Compare the Strength of Intermolecular Forces:**
- Among the gases analyzed, ammonia has the strongest intermolecular forces due to hydrogen bonding.
- Hydrogen, nitrogen, and helium exhibit much weaker London dispersion forces.

5. **Conclusion:**
- Since ammonia has the strongest intermolecular forces, it is expected to have the highest value of Van der Waals constant 'a'.

### Final Answer:
The gas expected to have the highest value of Van der Waals constant 'a' is **Ammonia (NH₃)**.

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