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

Explanation

The given salt is alkaline to litmus. Therefore, X is a salt of a strong base and a weak acid. Also, when X is strongly heated, it swells to form substance Y. Therefore, X must be borax.
When borax is heated, it loses water and swells to form sodium metaborate. When heating is continued, it solidifies to form a glassy material Y. Hence, Y must be a mixture of sodium metaborate and boric anhydride.
`underset("Borax "(X))underset()(Na_(2)B_(4)O_(7))+7H_(2)Ooverset("water")rarrunderset("Sodium hydroxide")underset()(2NaOH)+underset("Orthaboric acid")underset()(4H_(3)BO_(3))`
`underset("Borax"(X))underset()(Na_(2)B_(4)O_(7).10H_(2)O)overset(Delta)rarrunderset("Sodium metaborate")underset()(Na_(2)B_(4)O_(7))overset(Delta)rarrunderset(("Glassy material"))underset("Boric anhydride")underset()(B_(2)O_(3))+2NaBO_(2)`
When concentrated acid is added to borax, white crystals of orthoboric acid (Z) are formed.
`underset("BOrax"(X))underset()(Na_(2)B_(4)O_(7).10H_(2)O)+H_(2)SO_(4)overset(Delta)rarrNa_(2)SO_(2)+underset("Orthoboric acid (Z)")underset()(4H_(2)BO_(2))+5H_(2)O`