How would you know if a cyclic organic molecule is planar?

Hint: When the cyclic organic molecule is planar in nature then the compound is said to be an aromatic compound. For a compound to be aromatic in nature, it should follow Huckel’s rule. Planar means the compound is flat and all the carbon atoms are present in one single plane.

Complete step by step answer:
Many of the organic compounds are cyclic in nature but they are not always considered as the aromatic compound. Some cyclic compounds are non-aromatic in nature.
The aromatic compounds are defined as those compounds which contain one or more than one ring with delocalization of pi-electrons. Non-aromatic compounds lack pi-electron delocalization.
The aromaticity is the property of the conjugated cycloalkenes which increases the stability of the molecule because of delocalization of electrons present in pi-pi orbitals.
The aromatic compound follows Huckel’s rule which says that for a compound to be aromatic, it should follow $(4n + 2)\pi $ electrons where the n is the integer with positive value which include zero also. The aromatic compound should be planar in nature where p-orbitals are more or less parallel and interact with each other.
The cyclic organic compound is planar in nature when the carbon present in the ring is $s{p^2}$ hybridized and all carbon atoms lie in the same plane.

Note:
Not all the rings of other sizes have $s{p^2}$hybridization but for a six membered ring the carbon is always $s{p^2}$hybridized. When the ring compound shows chair conformation or half-chair conformation, then the compound is not planar in nature.