posted by saphire .
Silver chloride, AgCl, would be least soluble in
This is the common ion effect.
AgCl(s) --> Ag^+(aq) + Cl^-(aq)
Ksp = (Ag^+)(Cl^-)
Adding extra Ag^+ from AgNO3 increases (Ag^+) and that shifts the equilibrium to the left (to fewer ions and more solid) and that makes it less soluble. HCl will do the same thing as will ZnCl2. NaNO3 is the only one (excluding the effect of activity versus concn) that will not affect the solubility. So AgNO3 gives you 1 mole Ag^+/L, HCl gives 1 mole Cl^-/L but ZnCl2 will give two moles ZnCl2/L; therefore, the ZnCl2 will make it less soluble than the others.