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JEE Main levelSingle correct optionDifficulty 2 of 3mt128

The graphite anodes of a Hall-Heroult cell must be replaced from time to time because

  1. Aliquid aluminium is deposited on the anodes and dissolves them
  2. Bcryolite is reduced at the anode forming carbides
  3. Coxygen liberated at the anode burns the graphite to CO and
  4. Dfluorine liberated at the anode converts graphite into soluble fluorides

Answer: C

At the anode oxide ions are discharged to oxygen, which reacts with the hot graphite: overall . Carbon is thus consumed and the anodes wear away. Aluminium forms at the cathode, not the anode.
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