I think the correct answer would be the last option. The ocean zone which has the lowest water pressure would be the uppermost zone which is the Epipelagic zone. This zone is also called as the euphotic zone or the sunlit zone. It is the region which receives the most sunlight in order to allow photosynthesis.
The epipelagic zone is the zone which exists over the surface of water. It is also called as the sunlight zone as it receives the maximum and direct sunlight from the sun. It is also called as photosynthetic zone as the sunlight is utilized by the plants and small phytoplanktons to conduct photosynthesis. This zone exhibit lowest water pressure as it lies in the superficial layers of the water body.
