The pyramid of biomass in the sea is -

The correct answer is Option (3) → Inverted

A pyramid of biomass shows the mass of living matter at each trophic level. On land it is usually upright, because the producers outweigh the herbivores. In the sea the phytoplankton are small and are eaten very fast, so at any moment their biomass is less than that of the fishes feeding on them. The base becomes the narrowest bar.

Option (1) Always upright — Incorrect. It is the pyramid of energy that is always upright; the biomass pyramid can be inverted.

Option (2) Upright — Incorrect. Upright is the usual shape on land, not in the sea.

Option (3) Inverted — Correct. The pyramid of biomass in the sea is generally inverted, because the biomass of fishes far exceeds that of phytoplankton at any time. The phytoplankton are small and short-lived but multiply fast, so a small standing crop supports a larger one.

Option (4) Neither inverted nor upright — Incorrect. A pyramid has to be one or the other; there is no third shape.

NCERT Extract:
Ecological Pyramids – “… The pyramid of biomass in sea is generally inverted because the biomass of fishes far exceeds that of phytoplankton.”