The van't Hoff factor (i) is a measure of the number of particles that a solute dissociates into when dissolved in a solvent. For a compound like NaCl that completely dissociates in water, the van't Hoff factor is 2.

This is because when NaCl dissolves in water, it breaks up into its constituent ions, Na+ and Cl-. Each NaCl molecule gives rise to two ions, so the van't Hoff factor is 2.