Which of the following are acid-base reactions?
a. K₃P(s) + 2O₂(g) → K₃PO₄(s)
b. 2Na(s) + 2HCl (aq) → 2NaCl(aq) + H₂(g)
c. Na₂S(aq) + 2HCl(aq) → 2NaCl(aq) + H₂S(g)
d. 3KOH(aq) + H₃PO₄(aq) → K₃PO₄(aq) + 3H₂O(1)
e. Mg(s) + Cl₂(g) → MgCl₂(s)
f. MgO(s) + 2HCl(aq) → MgCl₂(aq) + H₂O(l)