An alkali metal A gives a compound B (molecular mass = 40) on reacting with water. The compound B gives a soluble compound C on treatment with aluminium oxide. Identify A, B and C and give the reactions involved. 

Explanation

The available data suggests that the metal 'A' sodium (Na). It reacts with water to form sodium hydroxide 'B' with formula NaOH. On reacting with aluminium oxide, the compound 'B' forms sodium metaaluminate 'C'.
The chemical equations for the reactions are :
`underset("[A]")(2Na(s))+2H_(2)O(aq)rarrunderset("[B] with molecular mass = 40")(2NaOH(aq)+H_(2)(g))`
`2NaOH(aq)+Al_(2)O_(3)(s)rarrunderset("[C] sod. metaaluminate")(2NaAlO_(2)(aq)+H_(2)O(aq))`