which of the following coordination compounds will most likely form a precipitate when treated with an aquesous solution of silver(l) nitrate?

A) [Cr(NH3)2CL3]
B) [Cr(NH3)6]Cl3
C) [Cr(NH3)Cl]SO4
D) Na3[Cr(CN)6]
E) Na[CrCl6]

i think its either a or b but i don't know which exactly is right?

Pick the one in which the Cl is not part of the coordination sphere with Cr.

that would be choice B right?

right. If the Cl is coordinated, it is a covalent bond and the covalent bonds doesn't allow the pptn of AgCl easily. Sometimes one can see a light cloudy color but not much. Outside the coordination sphere it is an ionic compound and the Ag^+ + Cl^- ==> AgCl proceeds easily.