Question

An acid (X) reacts with a base (Y) to produce Mg3(PO4)2. What are X and Y?
X = H3PO3; Y = Mg(OH)2
X = H3PO4; Y = Mg(OH)2
X = H3PO4; Y = Ca(OH)2
X = H3PO3; Y = Ca(OH)2

Answer 1

X = H3PO4; Y = Mg(OH)2.

Reason: H3PO4 (phosphoric acid) can furnish PO4^3− (phosphate) ions; H3PO3 (phosphorous acid) is dibasic and gives phosphite, not PO4^3−. Balanced equation:
2 H3PO4 + 3 Mg(OH)2 → Mg3(PO4)2 + 6 H2O.