Give reason for the following`:`
(a) Sodium metal is kept immersed in kerosene.
(b) Blue colour of copper sulphate disappers when a some aluminium powder is added in it.

Explanation

(a) Sodium metal is so reactive that it reacts vigorously with the oxygen ( of air). It catches fire and starts burning when kept open in the air. Sodium metal is stored under kerosene oil to prevent its reaction with oxygen, moisture and carbon dioxide of air.
(b) When aluminium powder is put in copper sulphate solution, then the blue colour of copper sulphate solution fades gradully due to the formation of colourless aluminium sulphate solution.
`underset("Blue")(3CuSO_(4)(aq))+2Al(s) overset("Displacement")(rarr) underset("Colourless")(Al_(2)(SO_(4))_(3)(aq))+3Cu(s)`
Since Al is more reactive than Cu, it displaces Cu from `CuSO_(4)` solution and forms colourless `Al_(2)(SO_(4))_(3)`