Let the solubility of CaF2 in 0.1MNaF is ' S' mol L−1 CaF2(s)⇌SCa2+(aq)+2S2F−(aq) NaF(aq)⇌0.1MNa++0.1MF−(aq) [F−]=2S+0.1 Ksp of CaF2=[Ca2+][F−]2 =[S][2S+0.1]2 =5.3×10−11=[S][2S+0.1]2 ⇒5.3×10−11=[S][0.1]2[∵2S≪0.1] [S]=(0.1)25.3×10−11=5.3×10−9molL−1