The correct option is **B. it makes bauxite melt at a lower temperature**. ### Detailed Explanation: 1. **Understanding the Process**: - The extraction of aluminum from bauxite involves a process called electrolysis. Bauxite is primarily composed of aluminum oxide (Al₂O₃), which has a very high melting point (around 2050°C). To extract aluminum efficiently, we need to lower this melting point to make the process more energy-efficient and practical. 2. **Role of Cryolite**: - Cryolite (Na₃AlF₆) is added to the aluminum oxide during the electrolysis process. The primary reason for adding cryolite is that it acts as a flux. A flux is a substance that helps to lower the melting point of another substance. When cryolite is mixed with aluminum oxide, it forms a molten solution that can melt at a much lower temperature (around 950-1000°C). This significant reduction in temperature is crucial because it reduces energy consumption and costs associated with the electrolysis process. 3. **Conductivity**: - While it is true that cryolite can improve the conductivity of the molten mixture, the primary reason for its use is the reduction of the melting point. Therefore, option A, which states that it makes bauxite a better conductor of electricity, is not the main reason for its addition. 4. **Purity of Aluminum**: - Option C states that cryolite makes aluminum purer. While the use of cryolite can help in the overall efficiency of the electrolysis process, it does not directly affect the purity of the aluminum produced. The purity of aluminum is more influenced by the quality of the bauxite and the electrolysis conditions rather than the presence of cryolite. 5. **Oxidation Prevention**: - Option D suggests that cryolite prevents aluminum from getting oxidized. This is not accurate. The electrolysis process itself is designed to reduce aluminum ions to aluminum metal, and while the molten aluminum can be susceptible to oxidation, cryolite does not play a direct role in preventing this oxidation. ### Summary of Key Points: - **Cryolite lowers the melting point** of aluminum oxide, making the electrolysis process more efficient. - The melting point of the cryolite-aluminum oxide mixture is significantly lower than that of pure aluminum oxide. - While cryolite can improve conductivity, its primary function in this context is to reduce melting temperature. - Cryolite does not directly influence the purity of aluminum or prevent oxidation. ### Revision Summary: - Cryolite is used in aluminum extraction to lower the melting point of aluminum oxide. - It allows the electrolysis process to occur at a more manageable temperature, saving energy. - Other options (A, C, D) do not accurately describe the primary role of cryolite in the extraction process.