Hi Naveen

Benthic zone is the  layer  closer to the bottom of a water body, it is ecological zone located at the bottom of any marine or freshwater body like river, ocean,
whereas
Pelagic zone refers to the uppermost layers of a water body . The pelagic zoneconsists of the water column of the open ocean, andcanbe further divided into regions by depth .

For example,
Benthic zone is part of Ocean layer that is closer to the bottom of the water body, whereas if we talk about Pelagic zone then it is a layer which includes the free water column which interacts with the surface layers of a water body.

I hope that you find this helpful


Thank you