Explanation

(a)
A compound is said to have aromatic character if ring system is planar (with $p$-orbital) and there is complete delocalisation of $\pi$-electrons (lone pair may be taken for delocalisation as relay electrons). This is true is conjugated cyclic system.
[image:13_image297.emf]
Huckel rule is followed by when electrons used in delocalisation=$(4\pi + 2)$
(including lone-pair)
Where, $n$=0, 1, 2, 3,….
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ring is planar
ring is not conjugated
delocalisation of $\pi$-electrons is not possible after $C_{4}.$
$(4\pi + 2)\pi$-electrons=4
Hence, it is not aromatic.