Question

Orthoboric acid when heated to red hot gives:

• A. Metaboric acid
• B. Pyroboric acid
• C. Boron and water
• D. Boric oxide

Answer 1

The correct option is D Boric oxide

Orthoboric acid, $H_{3}B{O}_3$ is a white crystalline solid, with soapy touch. It is sparingly soluble in water but highly soluble in hot water.
On heating, orthoboric acid above 370 K forms metaboric acid, $HB{O}_2$ which on further heating yields boric oxide, $B_2{O}_3$.
$H_{3}B{O}_3\stackrel{{100}^{\circ }C}{⟶}HB{O}_2\stackrel{\Delta }{⟶}{B}_2{O}_3$​
Hence correct option is d.