Which is least likely to cause eutrophication? pesticides phosphates fertilizers nitrates

The answer is: pesticides.

Eutrophication is a process by which nutrients, particularly phosphorus and nitrogen, become highly concentrated in a water, leading to increased growth of algae or cyanobacteria.

Fertilizers contain phosphorus and nitrogen, pesticide do not.

NPK ratio system is a conventional shorthand for the ratio of the nitrogen (N), phosphorus (P) and potassium (K) in a fertilizer.

Eutrophication is a serious environmental problem.

it is the most commonly accepted one