Let, solubility of Ca(OH)2 in pure water =Smol∕L ‌Ca(OH)2⇌Ca2++2OH− ‌Smol∕L‌‌2×S(mol∕L) =‌‌[Ca2+][OH−]2=S×(2S)2=4S3(mol∕L) The expression of Ksp can also be written as, Ksp‌‌=xx⋅yy⋅Sx+y ‌‌=11⋅22⋅S1+2 ‌‌=4S3 Ksp‌‌=xx⋅yy⋅Sx+y ‌‌=11⋅22⋅S1+2 ‌‌=4S3‌‌[∵‌ For ‌Ca(OH)2:x=1,y=2] x and y are the coefficients of cations and anions respectively S‌‌=(‌