Question

Which among the following species act both as an acid as well as a base?

• A. ${SO}_4^{2-}$
• B. $H{SO}_4^{-}$
• C. ${PO}_4^{3-}$
• D. ${NH}_3$

Answer 1

Answer: (B), (D)

${NH}_3$
$H{SO}_4^{-}$

Sulphate ion $\left(S{O}_4^{2-}\right)$ acts as a very weak base and phosphate ion $\left(P{O}_4^{3-}\right)$ effectively acts as a base.

However, Ammonia $\left(N{H}_3\right)$ can act as the base by accepting the proton and it can also act as an acid by accepting a lone pair of electrons. Thus it is amphoteric in nature

Bisulphate ion $\left(HS{O}_4^{-}\right)$ can either donate or accept a proton and form sulphate ion and sulphuric acid respectively. Thus, it is amphoteric in nature and can act as both acid and base.

Hence, the correct answer is both option (B) and option (D).