Classify each of the following reactions as a decomposition reaction, combination reaction, combustion reaction or displacement reaction.
1. When solid calcium oxide, CaO, is exposed to gaseous the sulfur trioxide, SO3, then the solid calcium sulfate, CaSO4, is produced.
2. When the calcium metal (solid) reacts with the water to form a solution of hydrogen gas and calcium hydroxide, Ca (OH)2.
3. When solid sodium hydrogen sulfite, NaHSO3, is heated, sulfur dioxide gas, SO2; solid sodium sulfite, Na2SO3; and the water vapor are produced.
4. When the Magnesium reacts with bromine to give magnesium bromide, MgBr2.