Answer:
I think it is iron conducts electricity and heat
1) Chemical equation of the equilibrium
BaCrO4⇄ Ba (2+) + CrO4 (2-)
2) Ksp equation
Ksp = [Ba(2+)] [CrO4 (2-)]
where Ksp = 1.0 * 10^ - 10 and [Ba(2+)] = [CrO4(2-)] = x
3) Calculations
1.0 * 10^ -10 = x * x
=> x^2 = 1.10 * 10^-10
=> x = √[1.0 * 10^ -10] = 0.000010
Answer: [Ba(2+)] = [CrO4(2-)] = 0.00001 M
Light cannot pass though matter BUT, matter is technically atoms, which are mostly space with a few, moving objects.