The Hoff factor (i) for a compound represents the number of particles (ions) that the compound dissociates into when dissolved in a solvent. For AlCl3 (aluminium chloride), it dissociates into three ions in water: one aluminium ion (Al3+) and three chloride ions (3Cl-).

Each aluminium chloride molecule generates four particles (1 Al3+ and 3 Cl-) in the solution. Therefore, the Hoff factor for AlCl3 is 4.

Mathematically, the Hoff factor can be calculated as:

Hoff factor (i) = Number of particles in solution formed from one solute molecule/compound

For AlCl3, i = 4