Chromium (III) iodate has a Ksp at 25°C of 5.0 x 10–6.

Question

125 mL of a solution contains 0.0050 mol L–1 Cr (III) ion.

What is the molar solubility of chromium (III) iodate at 25°C?
a.
8.4 x 10–2 mol L–1
b.
2.2 x 10–3 mol L–1
c.
6.3 x 10–2 mol L–1
d.
2.1 x 10–2 mol L–1

I know how to find solubility but i don't know what to do with the extra information :
125 mL of a solution contains 0.0050 mol L–1 Cr (III) ion.

Answer 1

ignore it. It's irrelevant.
Ksp = (x)(3x)^3 and solve for x = solubility.