The van der Waals constant ……………….. Measures the forces of attraction between the molecules of a gas.

Explanation

To answer the question regarding the van der Waals constant that measures the forces of attraction between the molecules of a gas, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding van der Waals Constants**: The van der Waals equation accounts for the behavior of real gases and includes two constants, A and B. Here, A represents the attraction between gas molecules, while B accounts for the volume occupied by the gas molecules.

2. **Identifying the Constant for Attraction**: The question specifically asks about the constant that measures the forces of attraction. In the context of the van der Waals equation, it is the constant 'A' that quantifies the attractive forces between gas molecules.

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