For the first reaction, a compound HI was broken down to two simpler molecules H₂ and I₂.
It means that the first reaction is classified as a decomposition reaction.
For the second reaction, something similar happens, sodium chloride is broken down to sodium and chlorine.
The second reaction is classified as a decomposition reaction.
For the third reaction, there is a double susbtitution, carbonate is separated from magnesium and then linked with hydrogen, and chloride is separated from hydrogen and then linked with the magnesium.
It means that the third reaction is a double displacement reaction.
For the fourth reaction, sulfate is separated from hydrogen and then linked with zinc.
It means that the fourth reaction is a simple displacement reaction.
For the fifth reaction, nickel and chlorine form nickel chlorine, which is a more complex molecules.
It means that the fifth reaction is a synthesis reaction.
For the sixth reaction, calcium carbonate is broken down to calcium oxide and carbon dioxide, which are simpler molecules.
It means that sixth reaction is a decomposition reaction.
For the seventh reaction, there is a double substitution from the reactants to form the products.
It means that this is a double displacement reaction.
For the last reaction, two simpler molecules form a more complex molecule.
It means that this is a synthesis reaction.