Question

$KMn{O}_4$ (acidic/alkaline) is not decolourised by:

• A. mohr salt
• B. oxalic acid
• C. benzene
• D. propene

Answer 1

Answer: (C)

benzene

The aromatic compound which have a double or triple bond in the side chain decolourise acidic/alkaline $KMn{O}_4$. Benzene does not decolourise the acidic/alkaline $KMn{O}_4$ due to the delocalisation of $\pi$-electrons.

While propene decolourised the alkaline $KMn{O}_4$ due to the presence of double bond. Ferrous ammonium sulphate and oxalic acid decolourised the $KMn{O}_4$ in acidic medium.

$2KMn{O}_4+10FeS{O}_4+8H_{2}S{O}_4⟶K_{2}S{O}_4+2MnS{O}_4+5{Fe}_2{\left(S{O}_4\right)}_3+8H_{2}O$

$2KMn{O}_4+5C_2{H}_2{O}_4+3H_{2}S{O}_4⟶K_{2}S{O}_4+2MnS{O}_4+10C{O}_2+8H_{2}O$

Hence, option $C$ is the answer.