Answer:
The pollutants like heavy metals, organic solvents present in pesticides exist in small amounts in the atmosphere. During the process of the food chain, the concentration of these pollutants progressively keeps on increasing through different trophic levels. For example, fish eats a lot of planktonic growth may retain the pollutants in their tissues, birds or people that eat the fish might concentrate the pollutants still more. This process of accumulation of pollutants at different trophic levels is called as biomagnification. So, the correct answer is 'Assertion is correct but Reason is incorrect'.