Ans.
Abiotic factors are defined as non-living element present in an ecosystem. These factors include air, water, sunlight, sand, and minerals. Biotic factors include living organisms present in an ecosystem, such as plants, animals, microbes.
Gravels are clusters of crushed rocks or stone and represent abiotic factors. On the other hand, algae, plants, and fish aret biotic factors.
Thus, the correct answer is option B). 'gravel on the bottom of the aquarium.'
