The correct option is A I>II>III
In case of Halogens, I effect dominates over M effect. Hence they are electron-withdrawing in nature. The overall withdrawing power of Cl is more than F when attached to conjugated system even though F is more electronegative.
−Cl has three effects +M,−M,−I . In case of −Cl, +M weakens up due to 2p−3p overlapping (leading to pi bond). But it is not so in case of −F which involve to 2p−2p overlap which is more effective. So, +M effect of −F is more than −Cl.
Therefore, the correct order of electron density is:
I>II>III