In the electrolytic refining of silver:

The correct answer is Option (3) → the anode is impure silver, cathode is pure silver

In electrolytic refining the impure metal is made the anode and a strip of the pure metal is the cathode; both dip in a solution of a soluble salt of the same metal. For silver the bath is silver nitrate solution. At the anode silver dissolves; at the cathode pure silver deposits:

    Anode: \( \ce{Ag -> Ag+ + e-} \)     Cathode: \( \ce{Ag+ + e- -> Ag} \)

Less reactive impurities such as gold collect below the anode as anode mud.

Why the other options are incorrect

• Option (1) the anode is pure silver, cathode is impure silver — Incorrect. The electrodes are reversed; the metal to be refined must dissolve, so it has to be the anode.

• Option (2) the anode is platinum, cathode is pure silver — Incorrect. With an inert platinum anode no impure silver would dissolve, so nothing would be refined.

• Option (4) Both anode and cathode are platinum — Incorrect. With two inert platinum electrodes the impure silver is not in the cell at all; only silver ions already in the bath would deposit, and nothing would be refined.

Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.

NCERT (Pre-rationalised edition, 2022-23):
Electrolytic Refining – “In this method, the impure metal is made to act as anode. A strip of the same metal in pure form is used as cathode. They are put in a suitable electrolytic bath containing soluble salt of the same metal.”