The energy available to consumers determined by subtracting the energy used by plants from the total energy transformed by the process of photosynthesis.

The question is incomplete as it does not have the option which are:

A. Gross primary productivity

B. Net primary productivity

Net primary productivity

Explanation:

In a food chain, the producers are present at the bottom of the trophic level which absorbs the sunlight and converts the energy into other molecules called glucose by photosynthesis.

This glucose is then either used by the producers to form energy molecules called ATP for its metabolism or it could either store it in the form of the starch.

The energy which is absorbed by the producers per unit area in a unit time refers to the Gross primary productivity and the energy which is stored after the plant utilizes the glucose molecule to produce energy is known as the net primary productivity.

In other terms, the energy which is stored after energy used for metabolism from subtracting gross primary productivity is known as Net primary productivity.

Therefore, it is clear that only net primary productivity is utilized by the consumers and thus is the correct answer.