Question

When orthoboric acid $\left(H_{3}B{O}_3\right)$ is heated, the residue is:

• A. Boron
• B. Diborane
• C. Boric anhydride
• D. Borax

Answer 1

The correct option is C Boric anhydride

When heated (above 370 K), $H_{3}B{O}_3$ ​first forms metaboric acid $HB{O}_2$ and ​then boric anhydride.
$H_{3}B{O}_3\stackrel{{100}^{\circ }C}{⟶}HB{O}_2\stackrel{\Delta }{⟶}{B}_2{O}_3$​
Hence correct option is c.