The correct option is D Net primary productivityGross primary productivity×100
Ecological efficiency is the efficiency of transfer of energy from one trophic level to the other.
Ecological efficiency = Net primary productivityGross primary productivity×100
Productivity is the rate of biomass production. It can be classified into - (i) gross primary productivity (GPP) and (ii) net primary productivity (NPP).
Gross primary productivity of an ecosystem is the rate of production of organic matter during photosynthesis. Whereas, gross primary productivity minus respiration losses (R) is the net primary productivity (NPP) i.e., GPP – R = NPP.