Eight electron systems [8]-annulene (Cyclooctatetraene, COT)
Ten electron systems [10] annulenes
From electron count a ten-electron system should be a Huckel system and aromatic but the molecules listed below are not planar so none of them are aromatic.
In A there is no angle strain, but the 1,6-H atoms have a lot of steric hindrance between them so the molecule is forced out of planarity. The molecule has not been prepared.
B is a regular decagon and the angle should be 144, for greater than 120, so there is lack of planarity.
C also has some angle strain. How ever 10 electron planar, aromatic systems are known.