Bauxite (Al₂O₃·2H₂O) is the principal ore of aluminium. Haematite is Fe₂O₃, galena is PbS, cinnabar is HgS. Bauxite is refined by Bayer's process to produce alumina, then electrolytically reduced (Hall-Héroult process).
Explanation:
Oxidation is loss of electrons. Na loses an electron to become Na⁺, so it is oxidized. Options A, C, D involve gain of electrons (reduction). Oxidation also can be defined as gain of oxygen or loss of hydrogen. In the reaction, Na acts as reducing agent. Mnemonic: LEO (Loss of Electrons is Oxidation) GER (Gain of Electrons is Reduction).
Explanation:
Calcination is the process of heating a concentrated ore strongly in the absence or limited supply of air. It is typically used for carbonate ores to drive off volatile impurities like CO₂ and H₂O (e.g., CaCO₃ → CaO + CO₂). Roasting is done in the presence of excess air.
Explanation:
Stratospheric ozone absorbs harmful UV-B and UV-C radiation from the sun, protecting living organisms. Depletion by CFCs increases UV at surface. Infrared is absorbed by greenhouse gases.
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