What does the equation ΔT = K_f b represent?

The equation ΔT = K_f b specifically relates to the phenomenon of freezing point depression. In this equation, ΔT represents the change in temperature, K_f is the freezing point depression constant unique to the solvent, and b is the molality of the solute. When a non-volatile solute is added to a solvent, it disrupts the formation of the solid phase, effectively lowering the temperature at which the solvent will freeze compared to its pure state.

This is fundamental in understanding colligative properties, which are properties that depend on the number of solute particles in a solution rather than the identity of the solute. Freezing point depression is one of the key colligative properties along with boiling point elevation. The application of this formula allows one to calculate how much the freezing point is lowered, providing insight into the effects of solutes on solvent properties.

Thus, the representation of ΔT = K_f b indeed describes the depression of the freezing point when solute is added to a solvent, making it the correct answer.