Question

Which amongst the following is identified as a group III anion in the preliminary test?

• A. $C{l}^{-}$
• B. $N{O}_3^{-}$
• C. $S{O}_4^{2-}$
• D. $S^{2-}$

Answer 1

The correct option is C $S{O}_4^{2-}$

Sulphate ion $\left(S{O}_4^{2-}\right)$ is grouped as group III anion in the preliminary test as it does not produce any effervescence with dilute or concentrated sulphuric acid. However, $\left(C{l}^{-}\right)$ and $\left(N{O}_3^{-}\right)$ ions are classified as group II anions as they produce effervescence with concentrated sulphuric acid by releasing $HCl$ and $N{O}_2$ gases respectively. Also, $S^{2-}$ ion comes under group I anions as it releases $H_{2}S$ gas forming effervescence with dilute sulphuric acid.