(A) Teeth are made principally from the mineral hydroxyapatite, Ca₅(PO₄)₃OH, which can be dissolved in acidic solution such as that produced by bacteria in the mouth. The reaction that occurs is Ca₅(PO₄)₃OH(s) + 4 H⁺(aq) ⇌ 5 Ca²⁺(aq) + 3 HPO₄^2-(aq) + H₂O(l). Write the equilibrium constant expression K_c for this reaction.

(B) The steam–iron process is used to generate H₂(g), mostly for use in hydrogenating oils. Iron metal and steam [H₂O(g)] react to produce Fe₃O₄(s) and H₂(g). Write an expression for K_p for this reaction.