Explanation:
a) The presence of sulfate ions in a solution can be confirmed by the reaction of barium chloride in an acidic medium.
The balanced chemical equation of the reaction is shown below:

Hence, the white precipitate is barium sulfate and its formation with the ionic equation is shown below:

b) The presence of copper (II) ions can be confirmed by the following test:
Add potassium iodide solution to copper (II) solution.
Then a white ppt of cuprous iodide along with the liberation of iodine is observed and the entire solution attains brown color.
The chemical equation of the reaction is shown below:

c)(i)Due to this reaction, the blue color of the solution becomes white.
Reddish-brown copper is deposited at the bottom of the container.
(ii)In this reaction, zinc is oxidized.
d) (i) Copper is produced at the cathode.
(ii)
(iii) The reaction that takes place at the cathode is reduction.
Reduction is gaining of electrons.