A 100-ML Sample of Solution Contains 10 $\times$ 10^-5

Multiple Choice

A 100.-mL sample of solution contains 10.0 mmol of Ca²⁺ ion.How many mmol of solid Na₂SO₄ must be added in order to cause precipitation of 99.9% of the calcium as CaSO₄? The K_sp of CaSO₄ is 6.1 $\times$ 10^-5.Assume the volume remains constant.

A) 17.4
B) 10.0
C) 61.0
D) 71.0
E) 6.1