Which of the complex [Co(NH3)Cl3] and [Cr(NH3)5Cl]Cl2 will give precipitate with AgNO3 and why ?

When stuff dissolves in water you have ions floating around and bumping each other at random. If a bump makes something soluble, it promptly dissolves so you are never aware of it. If a bump makes something insoluble then it falls out and that is what we call precipitate. Silver chloride is insoluble, so any source of chloride ions precipitates silver chloride. So you have to figure out which of these dissolves into chloride ions and which does not.
en.wikipedia.org/wiki/Hexamminecobalt%28III%29_chloride
www.google.com/search?q=[Cr%28NH3%295Cl]Cl2