Ksp of any salt is equal to the multiplication of concentration of its ions. ‌‌ For ‌AgCl→Ag++Cl− Ksp=[Ag+][Cl−] ‌1.8×10−10=10−10[Cl−] ‌[Cl−]=‌
1.8×10−10
10−10
=1.8 Similarly, for AgBr [Br−]=‌
5×10−13
10−10
=5×10−3 For AgI I−=‌
8.3×10−17
10−10
=8.3×10−7 Lesser is the concentration of ion, more easily they get precipitated. So, order of precipitation is AgI >AgBr>AgCl