Write the balanced chemical equation for the following and identify the type of reaction in each case:
(a) Potassium bromide(aq) + Barium iodide(aq) → Potassium iodide(aq) + Barium bromide(s)
(b) Zinc carbonate(s) → Zinc oxide(s) + Carbon dioxide(g)
(c) Hydrogen(g) + Chlorine(g) → Hydrogen chloride(g)
(d) Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen(g)

(a) Potassium bromide(aq) + Barium iodide(aq) → Potassium iodide(aq) + Barium bromide(s)
2KBr(aq)+BaI2(aq) → 2KI(aq)+BaBr2(s)
In this reaction, both the reactants exchange ions to form two new products. Hence, it is a double displacement reaction
(b) Zinc carbonate(s) → Zinc oxide(s) + Carbon dioxide(g)
ZnCO3(s) → ZnO(s)+CO2(g)
In this reaction, a single substance yields two different products. Hence, it is a decomposition reaction
(c) Hydrogen(g) + Chlorine(g) → Hydrogen chloride(g)
H2(g)+Cl2(g) → 2HCl(g)
In this reaction, two different reactants react with each other to form a single product. Hence, it is called a combination reaction
(d) Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen(g)
Mg(s)+2HCl(aq) → MgCl2(aq)+H2(g)
In this reaction, more reactive Mg is replacing less reactive H. Hence, it is displacement reaction.