Explain why the colour of $KMnO_4$ disappears when oxalic acid is added to its solution in acidic medium.

(N/A) In an acidic medium,$KMnO_4$ acts as a strong oxidizing agent.
When oxalic acid $(H_2C_2O_4)$ is added to an acidic solution of $KMnO_4$,the purple-coloured permanganate ion $(MnO_4^-)$ is reduced to the colourless manganese$(II)$ ion $(Mn^{2+})$.
The balanced chemical equation for this redox reaction is:
$2MnO_4^- + 5H_2C_2O_4 + 6H^+ \rightarrow 2Mn^{2+} + 10CO_2 + 8H_2O$.
Since the product $Mn^{2+}$ is colourless,the characteristic purple colour of the $KMnO_4$ solution disappears.