Carbanion stability increases with electron-withdrawing groups (stabilize negative charge) and decreases with electron-donating groups (destabilize negative charge).
IV has CHO (strongly electron-withdrawing by inductive effect), most stable.
I has Br (weakly electron-withdrawing).
II is pure benzyl with resonance from ring.
V has CH₃ (weakly electron-donating).
III has OCH₃ (strongly electron-donating, destabilizes the carbanion).
The critical factor is inductive electron-withdrawing ability:
CHO > Br > H > CH₃ > OCH₃.
Therefore: IV > I > II > V > III.
