Class XII · Chemistry · Environmental Chemistry · Practice
Environmental Chemistry — practice
Board-style MCQs and past-paper short questions in the BIEK / Sindh Board pattern. Tap an option to check yourself instantly. Solved questions are at the bottom.
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Multiple-choice questions
Solved short questions & self-assessment (past papers)
Explain how acid rain forms and give two of its effects
SO₂ and NOx from burning fuels dissolve and oxidise in cloud water:
2SO₂ + O₂ → 2SO₃ ; SO₃ + H₂O → H₂SO₄ and 4NO₂ + O₂ + 2H₂O → 4HNO₃.
Effects: lakes turn acidic and fish die; marble/limestone buildings (CaCO₃) are corroded; forests & soil are damaged.
Why does one chlorine atom destroy so much ozone? (CFC mechanism)
UV splits a CFC: CCl₂F₂ + UV → Cl• + •CClF₂.
Cl• + O₃ → ClO• + O₂ then ClO• + O → Cl• + O₂.
The Cl• is regenerated, so it acts as a catalyst — a single Cl• can destroy tens of thousands of O₃ molecules.
What is eutrophication and how does it kill aquatic life?
Fertiliser runoff (nitrates/phosphates) over-feeds algae → an algal bloom covers the surface → algae die → microbes decompose them and use up the dissolved oxygen (high BOD) → fish suffocate.