What is a trophic level in a food chain or food web? 

The feeding relationship of an organism with others in the ecosystem.

A trophic level is the feeding relationship of an organism with others in the ecosystem. So the answer is (c).

The 10% law states that only about 10% of the energy from one trophic level is transferred to the next trophic level. This means that as energy moves up the food chain, it becomes increasingly less available to the organisms at each level.

Option (a) is incorrect because the physical size of an organism does not determine its trophic level.

Option (b) is incorrect because the number of organisms at a particular level in the food chain does not determine its trophic level.

Here are some examples of trophic levels:

• Producers are the first trophic level. They are the organisms that make their own food, such as plants, algae, and phytoplankton.
• Primary consumers are the second trophic level. They are the organisms that eat producers, such as herbivores.
• Secondary consumers are the third trophic level. They are the organisms that eat primary consumers, such as carnivores.
• Tertiary consumers are the fourth trophic level. They are the organisms that eat secondary consumers, such as top predators.

The 10% law has important implications for the structure of food chains and food webs. It means that there is a limit to the number of trophic levels that can exist in an ecosystem. If there are too many trophic levels, the energy available to the organisms at the top of the food chain will be too low to support them.