The answer given is (3)but I am not quite sure about it. I feel it's (2) Can anyone please explain this ? Thank you in advance kind human.
Structures 1 and 2 can be draws in alternate forms, specifically, in 1, a double bond between the C and the N atoms is an accepted alternate configuration. In 2, similarly, a double bond between the C and B atoms gives a different configuration. In both cases, the electron charge distribution is now "dispersed" differently relative to the original structure as drawn. Remember, these are all constructs, or our way of understanding such molecules. In structure 3 however, aromatic stability of the six member ring can not be changed without creating a 5-valent carbon atom and and 5-valent nitrogen atom. So there are no alternate structures for 3 as there are for 1 and 2.