(i) Metal sulphides and carbonates cannot be directly reduced to metals. They must first be converted to metal oxides because oxides are more easily reduced (e.g., by carbon or CO) to obtain the free metal.
(ii) Aluminium oxide (Al₂O₃) reacts with both acids and bases. It reacts with acids to form salt and water, and with bases (like NaOH) to form aluminate. Since it shows properties of both acidic and basic oxides, it is called amphoteric.
(iii) Na, K, Ca, and Mg are highly reactive metals (high reactivity). They readily react with oxygen, water, and other elements in nature, so they always exist as compounds and are never found in free (native) state.
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