Based on the given value of the ksp, what is the molar solubility of mg(oh)2 in 0.200 m naoh?

The Ksp refers to the equilibrium constant for a solid dissolving in an aqueous solution.
 Ksp=  5.61×10⁻¹¹  

The equation for this reaction is: 
 Mg(OH)₂ (s) ⇔ Mg²⁺ (aq) + 2 OH⁻ (aq) 

 And the associated equilibrium expression is: 
 Ksp = [Mg2+]  x  [OH–]² 
 Mg(OH)₂ its solid and because of that doesn't have molarity, so its not included.
 
Ksp             = [Mg²⁺]   x   [OH–]²
5.61x10⁻¹¹  = (x) (0.200)² 
x = 1,4025 x 10⁻⁹
 

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