Why is the pyramid of biomass generally inverted in the sea?

The correct answer is Option (1) → Biomass of fishes far exceeds that of phytoplankton.

A pyramid of biomass shows the total mass of living matter at each trophic level. On land it is usually upright, because producers have the largest biomass. In the sea the producers are tiny phytoplankton. At any one time their total mass is small, while the fishes that depend on them have a much larger total mass. So the pyramid stands upside down.

Option (1) Biomass of fishes far exceeds that of phytoplankton. — Correct. The biomass of fishes far exceeds that of phytoplankton. A larger mass at the top than at the base makes the pyramid inverted.

Option (2) Phytoplankton have a higher biomass than fishes — Incorrect. If phytoplankton had more biomass than fishes, the base would be the widest level and the pyramid would be upright, not inverted.

Option (3) There is no clear relationship between phytoplankton and fish biomass — Incorrect. There is a clear relationship: fishes depend on phytoplankton for food, and the book explains the shape by comparing their biomass.

NCERT Extract:
Ecological Pyramids – “… The pyramid of biomass in sea is generally inverted because the biomass of fishes far exceeds that of phytoplankton. … Pyramid of energy is always upright, can never be inverted, because when energy flows from a particular trophic level to the next trophic level, some energy is always lost as heat at each step.”