Huckel’s rule states, for a compound to be aromatic, the compound should be planar, cyclic, and should have (4n+2)π electrons that should be in continuous delocalization or an uninterrupted cyclic pi-electron cloud should be there. Here n=0,1,2…
So if we put n=0, we get 2π electrons
If we put n=1, we get 6π electrons
If we put n=2, we get 10 π electrons and so on.
Compound (A) is not aromatic due to presence of sp3 carbon between the rings.
Hence the compounds,B,C and D are Aromatic as they have (4n+2) delocalising π electrons associated to the ring.
Hence the number of aromatic compounds is 3
