According to werner theory primary, secondary and duel valency of central atom in Complex respectively
4Cl- satisfies primary valency, H2O and 2 en (bidentate)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 Cl- ligand acts as primary and secondary valency in given complex , so duel valency of Complex is 1