Eutrophication from nutrient ions

Steps:

• Eutrophication occurs when excess nutrients like nitrogen and phosphorus cause algal blooms, leading to oxygen depletion.
• Identify nutrient ions: nitrate (NO₃⁻) provides nitrogen; phosphate (PO₄³⁻) provides phosphorus.
• Common non-nutrient ions like Na⁺, Cl⁻, or SO₄²⁻ do not promote algal growth.
• Of four typical ions shown (e.g., NO₃⁻, PO₄³⁻, Na⁺, Cl⁻), only two are nutrients.

Why B is correct:

• B indicates 2 ions, aligning with the definition of eutrophication driven by N- and P-containing ions that fuel algal overgrowth and deoxygenation.

Why the others are wrong:

• A: Underestimates; both nitrate and phosphate contribute, not just one.
• C: Overestimates; only nutrient ions cause the effect, not three.
• D: Incorrect; non-nutrient ions like Na⁺ do not trigger eutrophication.

Final answer: B