Huckel’s rule states, for a compound to be aromatic, the compound should be planar, cyclic, and should have $(4\mathrm{n}+2)\mathrm{\pi }$ electrons that should be in continuous delocalization or an uninterrupted cyclic pi-electron cloud should be there. Here n=$0,1,2\dots$

So if we put n=$0$, we get $2$π electrons

If we put n=$1$, we get $6$π electrons

If we put n=$2$, we get $10$ π electrons and so on.

Compound (A) is not aromatic due to presence of ${\mathrm{sp}}^3$ carbon between the rings.

Hence the compounds,B,C and D are Aromatic as they have $(4\mathrm{n}+2)$ delocalising $\mathrm{\pi }$ electrons associated to the ring.

Hence the number of aromatic compounds is $3$