Answer. None of the reactions asked in the question are considered as synthesis reaction.
Explanation According to definition of synthesis reaction two of the reactants react together in order to form a single product . synthesis reaction are also known as combination reactions.
............(1)
where 'A' and 'B' are the reactants where 'AB' represent the product after reaction.
In part one, the reaction in which ammonium hydroxide reacts with potassium aluminium sulfate not only to give aluminium hydroxide but also gives ammonium sulfate , potassium hydroxide and water.
....(2)
In part two,magnesium sulfate reacts with ammonium hydroxide to give not only magnesium hydroxide but also ammonium sulfate.
...(3)
as in both reaction there are more than one product which means they are not synthesis reactions.