Explain the reason for the following: (i) Aluminium oxide is called an amphoteric oxide. (ii) An iron strip dipped in a blue copper sulphate solution turns the blue solution pale green. (iii) Hydrogen gas is not evolved when most metals react with nitric acid. (iv) Calcium does not occur in free state in nature. (v) Sodium or potassium metals are kept immersed under kerosene.

(i) As a reason we can say, as it reacts with both acids as well as bases to form salts. (ii) As a reason we can say, as Iron being more reactive than copper displaces copper from copper sulphate to form green ferrous sulphate solution (FeSO4). (iii) As a reason we can say, Nitric acid (HNO3) is a strong oxidising agent. Hydrogen gas produced gets oxidised to H2O. (iv) As a reason we can say, Calcium is a very-very reactive metal. As it reacts with the chemicals or chemical agents which is present in surroundings and occurs in combined state. (v) As a reason we can say, Sodium (Na) and potassium (k) are highly reactive metals. They do not react with kerosene. But it and react vigorously with oxygen in air and may even catch fire.