JEE Main levelSingle correct optionDifficulty 2 of 3mt033
In the Hall-Heroult cell the graphite anodes have to be replaced periodically because
Aoxygen liberated at the anode oxidises the carbon to CO and COX2
Bcryolite attacks graphite to form fluorocarbons that coat it
Caluminium ions react with graphite to form a carbide that dissolves
Dthe anode is reduced by the molten aluminium
Answer: A
At the anode OX2− is discharged and the nascent oxygen reacts with the hot graphite, giving a CO-COX2 mixture. The anode therefore burns away. The cathode lining is not consumed because aluminium is deposited there.