What does the van 't Hoff factor (i) indicate?

The van 't Hoff factor (i) is a crucial concept in colligative properties, which refers to the number of particles a solute generates in a solution. This factor specifically indicates the degree of ionization or dissociation of a solute when it dissolves in a solvent. For instances where an electrolytic solute, such as sodium chloride (NaCl), dissociates into its constituent ions (Na⁺ and Cl⁻), the van 't Hoff factor would be 2, reflecting that each formula unit results in two particles in solution.

This factor is particularly important in calculating properties like boiling point elevation and freezing point depression, as these properties depend on the total number of solute particles in a solution rather than the identity of those solute particles. The higher the degree of dissociation, the more significant the impact on these colligative properties.

In contrast, the other choices do not accurately describe what the van 't Hoff factor represents. The mass of solute in a solution relates to concentration, the rate of reaction pertains to kinetics, and temperature dependence of a solute would involve thermodynamic concepts, none of which are encapsulated by the van 't Hoff factor. Thus, identifying the correct choice highlights