1. A synthesis reaction is the combination of two or more reactants to form a product. This would be choice 3, the synthesis of sodium chloride from sodium and chlorine.
2. A double displacement reaction is a reaction where two composite reactants switch partners. This would be choice 4, where sodium hydroxide and hydrogen sulfate trade groups to become sodium sulfate and water.
3. A combustion reaction is the burning of a carbon based compound in the presence of oxygen to generate carbon dioxide and water. This would be choice 2, where methane reacts with oxygen.
4. A single displacement reaction involves the donation of an atom from a composite molecule to another atom to form a different molecule. This would be choice 1, where the hydrogen gives the chlorine to zinc through the reaction.
5. A decomposition reaction involves the breaking apart of a complex molecule into simpler atoms. This would be choice 5, where calcium hydroxide decomposes into calcium oxide and water.