Which one of the following pyramids can never be inverted?

The correct answer is Option (3) → Pyramid of energy

An ecological pyramid shows the trophic levels of a food chain, with the producers at the base. The pyramid of energy shows the energy at each level. When energy passes from one trophic level to the next, some of it is always lost as heat. So each level has less energy than the one below, and the pyramid is always upright.

(1) Pyramid of number — Incorrect. It can be inverted. One large tree can support thousands of insects, so the number of consumers is greater than the number of producers.

(2) Pyramid of biomass — Incorrect. It can be inverted. In the sea the biomass of fishes far exceeds that of the phytoplankton.

(3) Pyramid of energy — Correct. It is always upright because energy is lost at every step.

(4) Pyramid of trophic levels — Incorrect. This is not a separate type of pyramid. The three types are number, biomass and energy.

NCERT Extract:
Ecological Pyramids – …