An element A reacts with water to form a compound B which is used in white washing. The compound B on heating forms an oxide C which on treatment with water gives back B. Identify A, B and C and give the reactions involved. 

Explanation

Since the compound 'B' is used for white wash, it is calcium hydroxide and the element 'A' is calcium. Upon heating 'B' forms calcium oxiden 'C'. It reacts with water to give calcium hydroxide 'B' again.
`underset(("A"))(Ca(s))+2H_(2)O(aq) rarr underset(("B"))(Ca(OH)_(2)) (s) + H_(2)(g)`
`underset(( "B"))(Ca(OH)_(2)(s)) overset("heat")rarr underset(("C"))(CaO(s))+H_(2)O(g)`
`CaO (s) + H_(2)O(aq) rarrCa(OH)_(2)(s)`