JEE Main · 2021 · 17 Mar 2021 · Shift 2 · Environmental Chemistry

Eutrophication sets in when a water body receives more nutrient than it can absorb. Run-off from fertilised fields brings nitrate and phosphate into the water, and phosphate-containing detergents in domestic waste add more, so both of these are genuine reasons. The enrichment shows itself as a dense growth of algae and weeds whose decay consumes the dissolved oxygen, so a dense plant population belongs to the account of a eutrophic water body rather than contradicting it. A shortage of nutrients would hold plant growth back and prevent the condition altogether. The incorrect reason is the statement that water bodies lack the nutrients that would allow plant growth.