Which of the following can be most readily liquefied? The given value of `a` for `NH_(3)` is `4.17`, `CO_(2)` is `3.59`, `SO_(2)` is `6.71`, and `Cl_(2)` is `6.49`.

Explanation

To determine which of the given gases can be most readily liquefied, we need to analyze the provided values of 'a' for each gas. The 'a' value is a measure of the attractive forces between the molecules of a gas; a higher 'a' value indicates stronger intermolecular forces, which makes it easier to liquefy the gas.

### Step-by-Step Solution:

1. **List the Given Values of 'a':**
- For NH₃ (Ammonia), a = 4.17
- For CO₂ (Carbon Dioxide), a = 3.59
- For SO₂ (Sulfur Dioxide), a = 6.71
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