An example of inverted ecological pyramid is :

The correct answer is Option (3) → Pyramid of biomass of sea

Option (1) Pyramid of energy of forest — Incorrect. A pyramid of energy is always upright, because some energy is lost as heat at every step.

Option (2) Pyramid of energy of grassland — Incorrect. A pyramid of energy, in a grassland or anywhere, is always upright: some energy is lost as heat at each step, so a higher level always has less energy than the one below.

Option (3) Pyramid of biomass of sea — Correct. The tiny phytoplankton multiply very fast, so at any time their standing biomass is less than that of the fishes.

Option (4) Pyramid of number in a grassland — Incorrect. A grassland has very many grass plants, fewer herbivores and still fewer carnivores, so its pyramid of number is upright.

NCERT Extract:
Ecological Pyramids – “… In most ecosystems, all the pyramids, of number, of energy and biomass are upright, i.e., producers are more in number and biomass than the herbivores, and herbivores are more in number and biomass than the carnivores. Also energy at a lower trophic level is always more than at a higher level. There are exceptions to this generalisation: … The pyramid of biomass in sea is generally inverted because the biomass of fishes far exceeds that of phytoplankton.”