(a) Platinum, gold, and silver are used to make jewelry because they are highly resistant to corrosion, tarnish, and are very lustrous, meaning they maintain their shine and beauty over time; they are also considered “noble metals” due to their low reactivity with other elements.
(b) Sodium, potassium, and lithium are stored under oil because they are highly reactive metals that can easily react with air and moisture, potentially causing fires; the oil acts as a protective barrier to prevent this contact.
(c) Aluminium is used to make cooking utensils despite being highly reactive because it forms a protective layer of aluminium oxide on its surface when exposed to air, which prevents further corrosion and makes it safe for use in cooking.
(d) Carbonate and sulphide ores are usually converted into oxides during extraction because oxides are easier to reduce to the desired metal form during the smelting process; this conversion simplifies the extraction of the metal from the ore.