Question

Borax on heating strongly above its melting point melts to a liquid, which then solidifies to a transparent mass commonly known as borax-bead. The transparent glassy mass consists of:

• A. sodium pyroborate
• B. boric anhydride
• C. sodium metaborate
• D. boric anhydride and sodium metaborate

Answer 1

The correct option is D boric anhydride and sodium metaborate

Borax ($N{a}_2{B}_4{O}_7.10H_{2}O$) when dissolved in water forms orthoboric acid and an alkaline solution.

On heating strongly above its melting point, borax first loses its water and melts to a liquid, which then solidifies to a transparent mass, commonly known as borax-bead. This borax-bead is made of boric anhydride and sodium metaborate.

$N{a}_2{B}_4{O}_7.10H_{2}O\stackrel{\text{Heat}}{\to }{B}_4{O}_7\stackrel{\text{Heat}}{\to }2NaB{O}_2+B_2{O}_3$