The Concentration of Mg²⁺ in Seawater Is 5

Multiple Choice

The concentration of Mg²⁺ in seawater is 5.0 * 10^-2 M. What hydroxide concentration is needed to remove 90% of the Mg²⁺ by precipitation (For Mg(OH) ₂, K_sp = 1.2 * 10^-11.)

A) 5.1 * 10^-5 M
B) 4.9 * 10^-5 M
C) 4.7 * 10^-5 M
D) 4.5 * 10^-5 M
E) None of the above