Combined Electronic Effects

Ranking these cations requires weighing resonance delocalisation against hyperconjugation and inductive donation. The benzyl cation is stabilised by resonance into an entire aromatic ring, dispersing the positive charge over several carbons, and is the most stable. The allyl cation is also resonance-stabilised, but its charge is spread over only two terminal carbons of a small pi system, so it is somewhat less stable than benzyl yet still better than purely alkyl cations. The tertiary butyl cation, lacking any resonance, relies on the +I effect and nine hyperconjugative alpha hydrogens, which place it below the two resonance-stabilised cations. The ethyl cation, a primary species with minimal hyperconjugation and weak induction, is the least stable. The reversed and scrambled orderings in the other options contradict the principle that resonance outweighs hyperconjugation. This combined-effect ranking is a frequent JEE Advanced theme rooted in NCERT, and it rewards students who can weigh competing stabilising influences rather than applying a single rule blindly. A useful guiding principle is that delocalisation through a pi system, whether aromatic or allylic, almost always dominates over the localised donation of hyperconjugation and induction. Recognising which cation forms most easily also predicts the major product in reactions proceeding through carbocation intermediates. Plausibility check: arranging by the breadth of charge delocalisation, aromatic resonance beats allylic resonance, which beats hyperconjugation, which beats a bare primary cation, confirming the sequence.