Arrange the coefficients: 1) AL + → ALN 2) + → Fe + [3) Ba + HCL → + 4) HgO → Hg +

The reaction between aluminum and nitrogen results in the formation of nitrogen nitride. The reaction of the compound, so from two simple substances one complex is formed.
2Al + N2 = 2AlN.

The reaction between iron oxide and hydrogen produces iron and water. A substitution reaction, that is, between a simple and a complex substance, as a result of which a new simple substance is formed.
FeO + H2 = Fe + H2O.

The reaction between barium and hydrochloric acid is a substitution reaction. The reaction products are barium chloride and hydrogen.
Ba + 2HCl = BaCl2 + H2 ↑.

The decomposition of mercury oxide. From one complex substance, several simple or complex substances are obtained. The products of the decomposition reaction of mercury oxide are two simple substances – mercury and oxygen.
2HgO = 2 Hg + O2 ↑.