Question

Which of the following compounds is formed in borax bead test?

• A. Metaborate
• B. Tetraborate
• C. Triborate
• D. Orthoborate

Answer 1

The correct option is A Metaborate

Metaborate is formed in borax bead test.
On heating, borax loses water of crystallisation and swells up to form fluffy mass. On further heating, it melts to give a clear liquid which solidifies to a transparent glassy bead consisting of sodium metaborate and boric anhydride.
$N{a}_2{B}_4{O}_7\cdot 10H_{2}O\stackrel{△}{\to }N{a}_2{B}_4{O}_7+10H_{2}O\stackrel{{740}^{o}C}{⟶}\underset{\text{Sodium Metaborate}}{2NaB{O}_2}+B_2{O}_3$
$CuO+B_2{O}_3\to Cu(B{O}_2{)}_2\text{blue bead}$

Thus, Metaborate is formed.