Question

Which of them does not react with aqueous solution of $KMn{O}_4$ in presence of $H_{2}S{O}_4$ ?

• A. $N{O}_3^{-}$
• B. $S^{2-}$
• C. $I^{-}$
• D. $N{O}_2^{-}$

Answer 1

Answer: (A)

$KMn{O}_4$ oxidises
$H_{2}S(S^{2-})$ to $S$
$2Mn{O}_4^{-}+16H^{+}+5s^{2-}\to 2M{n}^{2+}+8H_{2}O+5s$
$KI(I^{-})$ to $I_2$
$2Mn{O}_4^{-}+16H^{+}+10I^{-}\to 2M{n}^{2+}+8H_{2}O+5I_2$
$KN{O}_2(N{O}_2)$ to $N{O}_3^{-}$
$2MN{O}_4^{-}+6H^{+}+5N{O}_2^{-}\to 2M{n}^{2+}+3H_{2}O+5N{O}_3^{-}$
In $N{O}_3^{-},N$ is present in its highest oxidation state $(+5)$, so it cannot be oxidised further.