An aq. Solution of a salt (x) is alkaline to litmus. On strong heating, it swell up to give a glassy material. When conc. `H_(2)SO_(4)` is added to a concentrated solution of x, white crystal of a weak acid separates out. Hence compound (x) is

Options

A. `Na_(2)SO_(4).10H_(2)O`
B. `MgSO_(4).7H_(2)O`
C. `Na_(2)B_(6)O_(11)`
D. `Na_(2)B_(4)O_(7).10H_(2)O`

Answer

D

Explanation

x is Borax
`Na_(2)B_(4)O_(7).10H_(2)O`
`Na_(2)B_(4)O_(7) + 7H_(2)O rarr 2NaOH + 4H_(3)BO_(3)`
`Na_(2)B_(4)O_(4) rarr underset(ubrace("Glassy bead"))(2NaBO_(2) + B_(2)O_(3))`
`Na_(2)B_(4)O_(7) + H_(2)SO_(4) + 5H_(2)O rarr Na_(2)SO_(4) + 4H_(3)BO_(3)`