KMnO4 acts as an oxidizing agent in an acidic medium. The number of moles of KMnO4 that will be needed to react with one mole of sulphide ions in an acidic solution is:
1. \(\frac{2}{5}\)
2. \(\frac{3}{5}\)
3. \(\frac{4}{5}\)
4. \(\frac{1}{5}\)

The reaction is as follows:

\(5 \mathrm{~S}^{2-}+2 \mathrm{MnO}_4^{-}+16 \mathrm{H}^{+} \longrightarrow 2 \mathrm{Mn}^{2+}+8 \mathrm{H}_2 \mathrm{O}+5 \mathrm{~S}\)

5 moles of S2- ions react with 2 moles of KMnO4 . So, 1 mole of S2- ion will react with \(\frac{2}{5}\) moles of KMnO4