What does each bar in the energy pyramid indicate?

The correct answer is Option (3) → The amount of energy present at that trophic level in a given time or annually per unit area

A pyramid of energy shows how much energy is present at each trophic level, with the producers at the base and the top consumers at the apex. Each bar stands for the energy content of one trophic level, measured in a given time or annually per unit area.

Option (1) The number of individuals at that trophic level — Incorrect. The number of individuals at each level is shown by a pyramid of numbers, not by an energy pyramid.

Option (2) The biomass of the standing crop at that trophic level — Incorrect. Biomass (the standing crop) at each level is shown by a pyramid of biomass.

Option (3) The amount of energy present at that trophic level in a given time or annually per unit area — Correct. Each bar in the energy pyramid indicates the amount of energy present at each trophic level in a given time or annually per unit area.

Option (4) The number of species present at that trophic level — Incorrect. Ecological pyramids count all organisms at a trophic level; they do not show the number of species at that level.

NCERT Extract:
Ecological Pyramids – “… 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. Each bar in the energy pyramid indicates the amount of energy present at each trophic level in a given time or annually per unit area.”

Figure 12.4 (d) An ideal pyramid of energy. Observe that primary producers convert only 1% of the energy in the sunlight available to them into NPP