In the electrolysis of alumina to obtain Aluminium metal, the cryolite is added mainly to

lower the melting point of alumina

The correct answer is option 1. lower the melting point of alumina.

The addition of cryolite \(Na_3AlF_6\)in the electrolysis of alumina \(Al_2O_2\) to obtain aluminum metal serves primarily to Lower the melting point of alumina.

Alumina (\(Al_2O_3\)) has a very high melting point, typically above 2000°C. This high melting point makes it impractical to directly electrolyze alumina using traditional methods. Cryolite (\(Na_3AlF_6\)) is added to alumina to form a eutectic mixture. A eutectic mixture is a mixture of substances that melts at a lower temperature than any of its constituents individually. By forming a eutectic mixture with alumina, cryolite significantly reduces the melting point of the mixture to a more manageable temperature, typically around 950-1000°C. This lower operating temperature is crucial for the industrial viability of the electrolysis process.

In the Hall-Héroult process, which is the primary method for the industrial production of aluminum, the electrolysis of alumina occurs in a molten state. Cryolite serves as an electrolyte, providing an environment conducive to the flow of electric current. The dissolved alumina in molten cryolite allows for the conduction of electricity necessary for the electrolysis process. The addition of cryolite increases the electrical conductivity of the molten mixture, facilitating the movement of ions during electrolysis.

Lowering the melting point of alumina through the addition of cryolite significantly reduces the energy requirements for the electrolysis process. Operating at a lower temperature translates to lower energy consumption, making the production of aluminum more economical and energy-efficient.

In summary, cryolite plays a crucial role in the electrolysis of alumina to obtain aluminum metal by lowering the melting point of alumina, facilitating the electrolysis process, and reducing energy requirements. This makes the production of aluminum feasible on an industrial scale.