One of the conditions stated by the Huckel’s rule for any system to be aromatic is that of planarity i.e., all atoms of the molecule must be present on the same plane. This rule is violated in structure (i) and (ii). The carbon atom indicated below are sp3 hybridised which disallow planarity (sp3 hybridised carbon is tetrahedral in geometry).

In (iii) the number of p electrons is 8. (2 per double bond). The Huckel’s rule allows 2, 6, 10, 14, ... etc. π electrons for any aromatic system. Since (iii) does not have (4n + 2) π electrons, therefore, it is not aromatic.