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.
Na2B4O7 + 7H2O → 2NaOH + 4H3BO3
When concentrated acid is added to borax, white crystals of orthoboric acid(Z) are formed.
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