In the electrolytic refining of copper, the electrolyte is a solution of acidified copper sulphate.

Option 1, acidified copper chloride, is not the correct answer because copper chloride is not commonly used as an electrolyte in the refining process.

Option 3, potassium chloride, is also not the correct answer as it is not commonly used in the electrolytic refining of copper.

Option 4, sodium sulphate, is not the correct answer either, as it is not typically used as the electrolyte in the refining process.

The correct answer, as given, is option 2, acidified copper sulphate. Copper sulphate is commonly used in the electrolytic refining of copper as it provides the necessary copper ions for the process. The addition of acid in the solution helps to increase the conductivity of the electrolyte and maintain the appropriate pH levels. Acidified copper sulphate allows for the transfer of copper ions from the anode to the cathode during the refining process.