J.R. S. answered 04/21/21
Ph.D. University Professor with 10+ years Tutoring Experience
To calculate solubility, solve the Ksp equation.
Mn(OH)2(s) <==> Mn2+(aq) + 2OH-(aq)
Ksp = [Mn2+][OH-]2
let x = [Mn2+] and then 2x = [OH-] since you get 2 OH- for each 1 Mn2+
2.00x10-13 = (x)(2x)2 = 4x3
x3 = 5x10-14
x = 3.7x10-5 M = [Mn2+] = molar solubility of Mn(OH)2