Question

Anodes need to be replaced from time to time during the electrolysis of alumina. Write scientific reason

Answer 1

Answer Anodes needs to be replaced during the electrolysis of the Alumina because they gets oxidized. 

Explanation 
During the Electrolysis of the Alumina, Oxygen is deposited at the anode. Now, Anode is made up of the graphite (or Carbon), thus carbon reacts with the Oxygen and forms its oxide.  As a result of this Oxidation, we needs to replace the anode from time to time.

Reaction at the Anode ⇒ 

 2O²⁻ - 4e⁻ ----------→ O₂

Now, this Oxygen reacts with the Carbon, 
∴ C + O₂ -----------→ CO₂


To prevent that oxidation, Anode are replaced from time to time. 


Hope it helps.

Answer 2

Explanation:

this photo can help you