Assertion: The compound tetraene has the following structural formula.

It is cyclic and has conjugated 8π-electron system but it is not an aromatic compound.

Reason (R) (4n+2)π electrons rule does not hold good for this compound and the ring is not planar.

1.  Both assertion and reason are true and the reason is the correct explanation of assertion.

2.  Both assertion and reason are true and the reason is not the correct explanation of assertion.

3.  Assertion is true but the reason is false.

4.  Assertion is false but the reason is true.

Hint: cyclooctatetraene is not a planar compound
 
According to Huckel rule Aromaticity is shown by compounds possessing the following characteristics
(i) Compound must be planar and cyclic
(ii) Complete delocalization of π electrons in the ring
(iii) Presence of conjugated (4n+2)π electrons in the ring where n is an integer (n=0,1,2,....)
cyclooctatetraene (given) has a tub-like structure. It loses planarity. The number of πe- delocalized is 8 and n is not an
integer. Hence, cycloctatetraene is a non-aromatic compound.
Thus, both assertion and reason are true and the reason is the correct explanation of assertion.