A certain salt (X) gives the following tests

(i) Its aqueous solution is alkaline to litmus.

(ii) On strongly heating it swells to give a glassy bead.

(iii) When concentrated sulphuric acid is added to a hot concentrated solution of (X), crystals of ${\mathrm{H}}_3{\mathrm{BO}}_3$ separate out. Identify the colour of these crystals.

$$\begin{gathered} \left(\mathrm{X}\right) \mathrm{is} \mathrm{borax}, {\mathrm{Na}}_2{\mathrm{B}}_4{\mathrm{O}}_7.10{\mathrm{H}}_2\mathrm{O} \\ \left(\mathrm{i}\right) {\mathrm{Na}}_2{\mathrm{B}}_4{\mathrm{O}}_7 + 7{\mathrm{H}}_2\mathrm{O} \rightleftharpoons \underset{(\mathrm{Strong} \mathrm{Base})}{2\mathrm{NaOH}} + \underset{(\mathrm{Weak} \mathrm{acid})}{4{\mathrm{H}}_3{\mathrm{BO}}_3} \end{gathered}$$

Due to presence of NaOH, the aqueous solution is alkaline to litmus.

$$\begin{gathered} \left(\mathrm{ii}\right) {\mathrm{Na}}_2{\mathrm{B}}_4{\mathrm{O}}_7.10{\mathrm{H}}_2\mathrm{O} \underset{\left(\mathrm{swells}\right)}{\overset{\mathrm{Heat}}{\to }} {\mathrm{Na}}_2{\mathrm{B}}_4{\mathrm{O}}_7 + 10{\mathrm{H}}_2\mathrm{O} \to 2{\mathrm{NaBO}}_2 + \underset{\left(\mathrm{Glassy} \mathrm{bead}\right)}{{\mathrm{B}}_2{\mathrm{O}}_3} \\ \left(\mathrm{iii}\right) {\mathrm{Na}}_2{\mathrm{B}}_4{\mathrm{O}}_7 + {\mathrm{H}}_2{\mathrm{SO}}_4 + 5{\mathrm{H}}_2\mathrm{O} \to {\mathrm{Na}}_2{\mathrm{SO}}_4 + \underset{\mathrm{White} \mathrm{crystals}}{4{\mathrm{H}}_3{\mathrm{BO}}_3} \end{gathered}$$