ANS:C - remains constant.

In a dilute solution, the activity coefficient of the solute typically decreases with the increase in the concentration of the solute. The activity coefficient (γ) quantifies the deviation of a solution's behavior from ideal behavior. In dilute solutions, the interactions between solute particles are minimal, and the solute behaves more like an ideal solute. As the concentration of the solute increases, the interactions between solute particles become more significant, leading to deviations from ideal behavior. Consequently, the activity coefficient decreases as the concentration increases. At infinite dilution, the activity coefficient approaches unity for many solutes. In this limit, the interactions between solute particles are minimal, and the solution behaves ideally. Therefore, the activity coefficient is unity at infinite dilution for many substances.