Balance the following chemical equations and identify the type of chemical reaction.
$(a)$ $Mg(s) + Cl_2(g) \to MgCl_2(s)$
$(b)$ $HgO(s) \xrightarrow{\text{Heat}} Hg(l) + O_2(g)$
$(c)$ $Na(s) + S(s) \xrightarrow{\text{Fuse}} Na_2S(s)$

(N/A) Balanced equation: $Mg(s) + Cl_2(g) \to MgCl_2(s)$. This is a Combination reaction because two reactants combine to form a single product.
$(b)$ Balanced equation: $2HgO(s) \xrightarrow{\text{Heat}} 2Hg(l) + O_2(g)$. This is a Decomposition reaction because a single reactant breaks down into two simpler products upon heating.
$(c)$ Balanced equation: $2Na(s) + S(s) \xrightarrow{\text{Fuse}} Na_2S(s)$. This is a Combination reaction because two reactants combine to form a single product.