According to werner theory primary, secondary and duel valency of central atom in  CrH2O6Cl3 Complex respectively

3Cl- satisfies primary valency,6H2O satisfies secondary valency and the ligand satisfy primary and secondary valency is called duel valency, that means ligand involved in calculation of primary and secondary valency. Hence no Cl-  ligand acts as primary and secondary valency in given complex CrH2O6Cl3 , so duel valency  of CrH2O6Cl3 Complex is 0