Question

Assertion: In Hall's process for the preparation of Al, graphite anode has a long life.

Reason: $O_2$ is liberated in the process at the graphite anode.

• A. Both Assertion and Reason are true and Reason is the correct explanation of Assertion
• B. Both Assertion and Reason are true but Reason is not the correct explanation of Assertion
  
• C. Assertion is true but Reason is false
• D. Assertion is false but Reason is true
• E. Both Assertion and Reason are false

Answer 1

The correct option is D Assertion is false but Reason is true

Molten $A{l}_2{O}_3+N{a}_{3}Ai{F}_6\left(Cryolite\right)+Ca{F}_2\left(Flurospar\right)+Al{F}_3$ is used.
The electrolysis of this mixture is carried out using carbon (graphite) electrodes. The $O_2$ liberated at the anode reacts with the graphite anode needs to be replaced periodically.
Thus, graphite anodes do not have long life.
The overall reactions are as follows :
Cathode : $A{l}^{+3}\left(melt\right)+3e^{-}\to Al\left(l\right)$.
Anode : $C\left(s\right)+O^{2-}\left(melt\right)\to CO\left(g\right)+2e^{-}$
$C\left(s\right)+2O^{2-}\left(melt\right)\to C{O}_2\left(g\right)+4e^{-}$