Aromatic ring : huckel's rule : 4n+2 , planar, least reactive
Antiaromatic ring : 4n , planar , most reactive
Nonaromatic ring : no planar , no 4n+2
How can you know a ring is planar or not ? Thanks .

Aromatic ring : huckel's rule : 4n+2 , planar, least reactive
Antiaromatic ring : 4n , planar , most reactive
Nonaromatic ring : no planar , no 4n+2
How can you know a ring is planar or not ? Thanks .
There is no trick to it... You just have to know which are and which aren't.