When 1 mol CrCl3.6H2O is treated with excess of AgNO3, 3 mol of AgCl are obtained. The formula of the complex is :
If we get 3 moles of AgCl, then it means that all three chloride ions are free and not bound to the complex because ligands bound to the complex do not separate out and form precipitates. So, the formula of the complex has to be [Cr(H2O)6]Cl3.