What are the necessary conditions for any system to be aromatic?

(N/A) compound is said to be aromatic if it satisfies the following three conditions:
$(i)$ It should have a planar structure.
$(ii)$ The $\pi-$ electrons of the compound must be completely delocalized in the ring.
$(iii)$ The total number of $\pi-$ electrons present in the ring should be equal to $(4n+2)$,where $n = 0, 1, 2, \ldots$ This is known as Huckel's rule.