Answer:
This is because if its visible accurate colour change.
Step-by-step explanation:
Potassium Permanganate(KMNO4)is a water soluble salt which loses its purple color as it oxidizes alcohols. This makes it easier for the reaction to be followed visually.
Chromic acid(H2CrO4) on the other hand is an acid which oxidizes amino acids. It however tends to give a false positive color change. This makes Potassium permanganate preferable.