Answer
$$Al(OH)_3(aq) + 3HCl(aq) \longrightarrow AlCl_3(aq) + 3 H_2O(l)$$
$$Mg(OH)_2(aq) + 2HCl(aq) \longrightarrow MgCl_2(aq) + 2 H_2O(l)$$
$$CaC{O_3}(aq) + 2HCl(aq) \longrightarrow CaCl_2(aq) + H_2CO_3(aq)$$
Work Step by Step
1. Find the amount of HCl necessary to react with one mol of each antacid.
(a) Has 3 $OH^-$: Needs 3 $H^+$
(b) Has 2 $OH^-$: Needs 2 $H^+$
(c) Has 1 $C{O_3}^{2-}$: Needs 2 $H^+$ in order to neutralize it.
2. Write the products. The first one is a salt made of the metal in the antacid and chloride ion, and the second one is the conjugate acid of the reaction.
