Given reasons:(a) Platinum, gold and silver are used to make jewellery.(b) Metals like sodium and potassium are stored under oil.

(a) Platinum, gold, and silver are used to make jewellery because of their bright and shiny surface (metallic luster). Moreover, they are low reactive metals that are resistant to corrosion.

(b) Metals like sodium and potassium are stored under oil because they are very reactive in nature, they react with oxygen present in the air. Thus to prevent fire, they are kept in the oil.