Why is HCI not used to make the medium acidic in oxidation reactions of KMnO4 in acidic medium?

The correct option is: KMnO₄ oxidises HCl into Cl₂ which is also an oxidizing agent

Detailed Explanation:
Potassium permanganate (${\mathrm{KMnO}}_4$) is a very strong oxidizing agent in an acidic medium. When conducting oxidation reactions using ${\mathrm{KMnO}}_4$ in an acidic medium, we need an acid that simply provides hydrogen ions ($H^{+}$) to facilitate the reaction without participating in any redox activity itself.

If hydrochloric acid ($\mathrm{HCl}$) is used to acidify the medium, the chloride ions (${\mathrm{Cl}}^{-}$) present in $\mathrm{HCl}$ are oxidized by the powerful ${\mathrm{MnO}}_4^{-}$ ions. The reaction converts the chloride ions into chlorine gas (${\mathrm{Cl}}_2$), according to the following chemical equation:

$2{\mathrm{MnO}}_4^{-}+10{\mathrm{Cl}}^{-}+16H^{+}\to 2{\mathrm{Mn}}^{2+}+5{\mathrm{Cl}}_2+8H_{2}O$

Because ${\mathrm{KMnO}}_4$ is consumed in oxidizing $\mathrm{HCl}$ to ${\mathrm{Cl}}_2$ (which is itself a strong oxidizing agent), the concentration of ${\mathrm{KMnO}}_4$ available for the primary oxidation reaction is reduced. Furthermore, the liberated ${\mathrm{Cl}}_2$ gas can interfere with the reaction and lead to unwanted side products. Therefore, $\mathrm{HCl}$ is not used, and instead, dilute sulfuric acid ($H_2{\mathrm{SO}}_4$) is preferred as it is stable against oxidation by ${\mathrm{KMnO}}_4$.