Asolution in equilibrium with solid barium phosphate (ba3(p o4)2) is found to have a barium ion concentration of 0.0005 m and a ksp of 3.4 x 10−23. calculate the concentration of phosphate ion. 1. 2.6x10−7 2. 1.04x10−6 3. 5.2x10−7 4. 1.3x10−7 5. 2.7x10−13

Answer is:  3. 5.2x10−7.
Balanced chemical reaction (dissociation): 
Ba₃(PO₄)₂(s) → 3Ba²⁺(aq) + 2PO₄³⁻(aq).
[Ba²⁺] = 0,0005 M.
Ksp(Ba₃(PO₄)₂) = 3,4·10⁻²³.
Ksp = [Ba²⁺]³ · [PO₄³⁻]².
3,4·10⁻²³ = (0,0005 M)³ · [PO₄³⁻]².
[PO₄³⁻] = √3,4·10⁻²³ ÷ 1,25·10⁻¹⁰.
[PO₄³⁻] = 5,2·10⁻⁷ M.
Ksp is the solubility product constant for a solid substance dissolving in an aqueous solution.

The correct answer is "hydrogen".