The correct answer is D. NPP.
Primary productivity is the rate at which energy is converted into biomass by autotrophs. Secondary productivity is the rate at which energy is converted into biomass by heterotrophs. GPP is the gross primary productivity, which is the total amount of energy that is fixed by autotrophs. NPP is the net primary productivity, which is the amount of energy that is left after autotrophs have respired.
NPP is mobile in nature because it is the energy that is available to heterotrophs, which can be animals, fungi, or bacteria. Heterotrophs can move around to find food, and they can also store energy in their bodies. This means that NPP can be transported from one place to another, and it can be used by organisms that are not directly involved in primary production.
Primary productivity is not mobile in nature because it is the rate at which energy is converted into biomass by autotrophs. Autotrophs are plants, algae, and some bacteria, and they are not able to move around. This means that primary productivity is only produced in the places where autotrophs live.
Secondary productivity is not mobile in nature because it is the rate at which energy is converted into biomass by heterotrophs. Heterotrophs are animals, fungi, and some bacteria, and they are not able to move around. This means that secondary productivity is only produced in the places where heterotrophs live.
GPP is not mobile in nature because it is the total amount of energy that is fixed by autotrophs. Autotrophs are plants, algae, and some bacteria, and they are not able to move around. This means that GPP is only produced in the places where autotrophs live.