The chemical that is added to reduce the melting point of the reaction mixture during the extraction of aluminium is :

Solution

Chemistry ma’am · 3 steps

Pure alumina melts above 2000 °C, so we dissolve it in molten cryolite and run the electrolysis near 950 °C.

1. The problem. In the Hall–Héroult process, purified alumina Al₂O₃ is reduced by electrolysis. Pure alumina melts at about 2050 °C and conducts poorly, so electrolysing it on its own would be very costly.
2. The fix. Alumina is dissolved in molten cryolite, Na₃AlF₆, often with a little CaF₂. The mixture melts at about 950 °C and conducts electricity much better.

   Substance	Formula	What it is
   Cryolite	Na₃AlF₆	flux added to lower the melting point
   Bauxite	AlOₓ(OH)₃₋₂ₓ	ore of aluminium (the raw material)
   Calamine	ZnCO₃	ore of zinc
   Kaolinite	Al₂(OH)₄Si₂O₅	clay, an impurity-rich aluminosilicate

3. So. The added chemical is cryolite, option (a).

The idea to keep. Remember the trio for aluminium: bauxite is the ore, alumina is what gets electrolysed, and cryolite (with CaF₂) is the solvent that lowers the melting point and improves conductivity.

Answer from the NTA final answer key. Solution by PrepWiser.