Introduction:
Equimolal solutions of A and B show depression in freezing point in the ratio 2:1. A remains in its normal state in solution. This implies that B undergoes some kind of association or dissociation in solution. The correct option is C, "associated." Let us understand the concept in detail.

Explanation:
1. Freezing Point Depression:
The freezing point of a solvent is lowered when a non-volatile solute is added to it. This phenomenon is known as freezing point depression. It occurs because the presence of solute particles disrupts the regular arrangement of solvent particles, making it more difficult for the solvent to freeze.

2. Colligative Properties:
Freezing point depression is a colligative property, meaning it depends on the number of solute particles rather than their nature. Therefore, the depression in freezing point is directly proportional to the concentration of the solute.

3. Equimolal Solutions:
Equimolal solutions are those which contain the same number of moles of solute per unit volume. In this case, let's consider equimolal solutions of A and B.

4. Depression in Freezing Point Ratio:
The given ratio of depression in freezing point is 2:1. This means that for the same concentration of A and B, the freezing point of the solvent is lowered twice as much when B is added compared to when A is added.

5. A Remains in its Normal State:
Since A remains in its normal state in solution, it does not undergo any association or dissociation. This implies that A does not break down into smaller particles or combine with other particles to form larger entities.

6. B is Associated in Solution:
In contrast, B undergoes association in solution. This means that individual particles of B combine together to form larger entities or aggregates. This association leads to a greater depression in freezing point compared to A.

Conclusion:
In equimolal solutions of A and B, the depression in freezing point ratio of 2:1 indicates that B undergoes association in solution, while A remains in its normal state. Therefore, the correct option is C, "associated."