Q1: Identify the correct statement with reference to the extractive metallurgy of aluminium.

ANS:A - The electrolyte consists of molten Na₃AlF₆ with approximately 1 to 8% Al₂O₃.

The electrolyte consists of molten Na3AlF6 with approximately 1 to 8% Al2O3. In the Hall-Héroult process, which is the primary method for aluminum extraction, the electrolyte typically consists of molten cryolite (Na3AlF6) with small amounts of alumina (Al2O3) added. The addition of alumina helps to lower the melting point of the cryolite and increases its conductivity. This molten electrolyte serves as the medium for the electrolytic reduction of alumina to aluminum metal. The other statements are incorrect:

• Approximately 80% of the aluminum deposited on the cathode comes from cryolite: This statement is incorrect because the aluminum metal is primarily deposited at the cathode from the reduction of alumina (Al2O3), not from cryolite.
• Sodium is deposited along with aluminum, but is immediately vaporized: This statement is incorrect because sodium is not deposited along with aluminum in the Hall-Héroult process. Instead, sodium ions are recycled in the electrolyte.
• Anode effect sets in when the cryolite concentration goes below 40%: This statement is incorrect because the anode effect occurs when the cryolite concentration is too high, causing a decrease in cell voltage efficiency. It does not occur when the cryolite concentration goes below a certain threshold.