Question

Which one of the following is a dibasic acid?

• A. $H_3{PO}_4$
• B. $H_3{PO}_3$
• C. $H_3{BO}_3$
• D. $H_3{AsO}_4$

Answer 1

Answer: (B)

$H_3{PO}_3$

$H_{3}P{O}_3$ has three hydrogen atoms but only two hydrogen atoms are joined through the oxygen atoms and are ionizable. The third hydrogen atom is linked to phosphorous-atom directly and is not ionizable.

The hydrogen-atom joined to the phosphorous-atom is reducing in nature and is not ionizable as a proton and therefore $H_{3}P{O}_3$ acts as a dibasic acid.