The correct order of the stoichiometries of AgCl formed when AgNO3 in excess is treated with the complexes: CoCl3.6NH3, CoCl3.5NH3, CoCl3.4NH3 respectively is:

The correct order of the stoichiometries of AgCl formed is 3, 2, 1.

CoCl3.6NH3 is [Co(NH3)6]Cl3, which has 3 ionizable Cl- ions.
CoCl3.5NH3 is [Co(NH3)5Cl]Cl2, which has 2 ionizable Cl- ions.
CoCl3.4NH3 is [Co(NH3)4Cl2]Cl, which has 1 ionizable Cl- ion.

Therefore, when treated with excess AgNO3, the number of moles of AgCl formed will be 3, 2, and 1 respectively.