JEE Main Chemistry Question (2026) — Solution

Step-by-step solution

A species is aromatic if it is cyclic, planar, fully conjugated (continuous cyclic overlap of p-orbitals) and contains (4n + 2)\, electrons (Huckel's rule). Let us analyse each species. 1,4-Benzoquinone: The six-membered ring has only 4 electrons (from the two C=C bonds); the two C=O groups are cross-conjugated and do not contribute to a continuous (4n + 2)\, ring system. Hence, it is non-aromatic. Tropylium cation: A planar, cyclic, fully conjugated seven-membered system with three C=C bonds and a positive charge (empty p-orbital). It has 6\, electrons, satisfying Huckel's rule with n = 1. It is aromatic. Phenanthrene: A fused tricyclic, planar, fully conjugated hydrocarbon with 14\, electrons. It obeys Huckel's rule with n = 3. It is aromatic. 1,2-Dihydronaphthalene: It contains an intact benzene ring fused to a partially saturated six-membered ring. Because of the benzene ring, the molecule as a whole is classified as aromatic. Cyclobutadiene dication: A planar, four-membered ring with one C=C bond and two positive charges (two empty p-orbitals), giving 2\, electrons. It satisfies Huckel's rule with n = 0. It is aromatic. Cyclohexadienyl anion (as drawn with a -CH_2- group): The sp^3 -CH_2- carbon breaks the continuous cyclic conjugation, so the ring is not fully conjugated. Hence, it is non-aromatic. Counting the aromatic species: tropylium cation, phenanthrene, 1,2-dihydronaphthalene and cyclobutadiene dication give a total of 4 aromatic species. Hence, the correct option is (2)\ 4.