Answer:
MG is less polar
Explanation:
The structures of crystal violet (CV) and malachite green (MG) are shown in Figures 1 and 2, respectively.
The obvious difference is that CV has an extra dimethylamino group (polar).
Alumina is a polar adsorbent, so it retains the more polar substances more strongly and they are eluted last.
MG is less polar than CV, so it is retained less strongly and is eluted first.
