Which of the following molecules, in pure form, is (are) unstable at room temperature ?
Order of stability is Aromatic > Non aromatic > Anti Aromatic.
Compound !!B!! and !!C!! are anti aromatic compounds because they have !!4n!! number of !!pi!! electrons conjugating in the ring. Compound !!A!! is non-aromatic because it as a !!sp^3!! hybridised carbon (non planar) while the the compound !!D!! is aromatic !!( 4n + 2)!! !!pi!! electrons conjugating in a planar ring.