Give reasons
(a) Platinum, gold and silver are used to make jewellery.
(b) Sodium, potassium and lithium are stored under oil.
(c) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking.
(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction.

Give reasons for the following. Platinum, gold and silver are used to make jewellery.

Aluminium is stable in air and water inspite of the fact that it is reactive metal. The reason is that a thin film of its oxide, if formed on its surface which makes it passive for further attack. The layer is so useful that in industry, it is purposely deposited by an electrolytric process called anodizing. Reaction of aluminium with oxygen is highyl exothermic and is called thermite reaction 2Al(s)+(3)/(2)O_(2)(g)rarr Al_(2)O_(3)(s), Delta H=-1670 kJ Thermite reaction finds applications in the metallurgical extraction of many metals from their oxides and for welding of metals. The drawback is that to start the reaction, high temperature is required for which an ignition mixture is used. Anodised aluminium is

Aluminium is stable in air and water inspite of the fact that it is reactive metal. The reason is that a thin film of its oxide, if formed on its surface which makes it passive for further attack. The layer is so useful that in industry, it is purposely deposited by an electrolytric process called anodizing. Reaction of aluminium with oxygen is highyl exothermic and is called thermite reaction 2Al(s)+(3)/(2)O_(2)(g)rarr Al_(2)O_(3)(s), Delta H=-1670 kJ Thermite reaction finds applications in the metallurgical extraction of many metals from their oxides and for welding of metals. The drawback is that to start the reaction, high temperature is required for which an ignition mixture is used. Thermite mixture used for welding is