The correct option is A g/m2
Productivity of an ecosystem refers to the rate at which organic matter/biomass is produced per unit area over a time period.
Solar energy from the sun is utilised by organisms like green plants, algae, etc to prepare their own food in the form of organic matter.
Primary production refers to the total amount of organic matter produced, per unit area of an ecosystem, by the producers via the process of photosynthesis.
It is expressed in terms of weight (g/m2) or energy (kcal/m2).
The rate of primary production per unit time is known as primary productivity and is expressed in terms of g/m2/year or kcal/m2/year.
Primary productivity can be categorised as gross primary productivity and net primary productivity.
Gross primary productivity refers to the rate of production of organic matter during photosynthesis. Net primary productivity refers to the remainder of the gross production which is left after its use by the producers in the process of respiration. Net primary productivity is the biomass that is available to the heterotrophs in an ecosystem for consumption.
Secondary productivity is the rate at which the consumers/heterotrophs synthesise new organic matter.
All types of productivity are measured in the unit g/m2/year or kcal/m2/year.