RRB ALP CBT I 25 Nov 2024 Shift 2 Paper

Concept:In electrolytic refining, a soluble salt of the metal is used as the electrolyte to carry metal ions between electrodes.Explanation:Electrolytic refining of copper uses acidified copper sulphate solution as the electrolyte.The electrolyte must supply copper ions, so $\mathrm{CuSO}_{4}$ is suitable.Impure copper is made the anode, and a pure copper sheet is the cathode.On passing current, copper dissolves from the anode as $\mathrm{Cu} \rightarrow \mathrm{Cu}^{2+} + 2e^{-}$.These copper ions move to the cathode and deposit as pure copper: $\mathrm{Cu}^{2+} + 2e^{-} \rightarrow \mathrm{Cu}$.Impurities either dissolve in the solution or settle below as anode sludge.Sodium sulphate and cuprous chloride do not provide the required copper ions effectively, and copper oxide is insoluble.Hence, copper sulphate is the correct electrolyte for this process.Answer:The electrolyte used is copper sulphate, so the correct option is D. $\mathrm{CuSO}_{4}$.