Assertion : Presence of large amounts of nutrients in water body causes excessive growth of planktonic algae.
Reason : It is due to biomagnification.

If both assertion and reason are true and reason is the correct explanation of assertion.

If both assertion and reason are true but reason is not the correct explanation of assertion

If assertion is true but reason is false

If both assertion and reason are false

Solution

If assertion is true but reason is false

Presence of large amounts of nutrients in water causes excessive growth of planktonic algae or free- floating algae. It is known as algal bloom as it imparts a unique colour to the water bodies. Algal bloom cause deterioration of the quality of water and fish mortality.

Biomagnification is the process by which a compound such as pollutant or pesticide increases its concentration in the tissues of organisms as it travels up the food chain.