What is corrosion of metals? 

Give reasons for the following: 

Carbonate and sulphide ores are converted into oxides before reduction. 

Give reasons for the following: 

Aluminium is rendered passive when it is dipped in conc.${\mathrm{HNO}}_3$

Give reasons for the following: 

Nonmetals do not displace hydrogen from acids. 

Give reasons for the following: 

An aqueous solution of ${\mathrm{CuSO}}_4$ cannot be stored in an iron vessel. 

Give reasons for the following: 

The surface of some metals becomes dull when left exposed to air for a long time.