A certain salt `(X)` gives the following tests :
(a) Its aqueous solution is alkaline to litmus.
(b) On strong heating, it swells up to give a glassy material `(Y)`.
(c) When conc. `H_(2) SO_(4)` is added to a hot concentrated solution of `(X)`, white crystal of a weak acid `(Z)` separates out.
Identify `(X), (Y) and (Z)` and write down the chemical equations for reaction at steps `a, b` and `c`.

Explanation

(i) Since, the alkaline solution of the given salt [X] is alkaline to litmus, it must be a salt of strong base and weak acid.
(ii) The salt [X] on heating swells up to a glassy material (Y). Therefore, [X] should be borax and [Y] a mixture of sodium metaborate and boric anhydride.
(iii) When conc. H2SO4 is added to a hot solution of borax [A], white crystals of orthoboric acid [Z] separate out. Hence, [X] = `Na_2 B_4 O_7 . 10 H_2 O , [Y] = NaBO_2 + B_2 O_3 and [Z] = H_3 BO_3`.
The reaction can be expressed as follows :