An epic is a long narrative poem.
It usually deals with a serious, grand, and heroic subject.
Its style is formal, dignified, and elevated.
Examples include The Iliad, The Odyssey, and Paradise Lost.
Assertion (A) is incorrect because it says that an epic is on a comic subject and told in an informal style.
That description does not define an epic.
Reason (R) is correct because it properly describes an epic as a long verse narrative on a serious subject in a formal and elevated style.
Therefore, (A) is not correct but (R) is correct.