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✅ Introduction Paragraph
Master your understanding of Environmental Chemistry with this CBSE Class 11 Chemistry MCQs – Online Practice Test focusing on Chemical Reactions in the Environment. These carefully designed multiple-choice questions strictly follow the NCERT Class 11 Chemistry syllabus, making them perfect for CBSE board exam preparation.
This topic covers key environmental reactions such as acid rain formation, ozone layer depletion, photochemical smog, and oxidation–reduction processes in the atmosphere and hydrosphere. Practicing these MCQs will help students strengthen conceptual clarity on the chemical interactions occurring in air, water, and soil.
Each question is accompanied by the correct answer and explanation, ensuring students learn not only the “what” but also the “why” behind every reaction. Use this quiz to evaluate your readiness, identify weak areas, and gain confidence before exams.
✅ Sample MCQs with Answers and Explanations
Q1. Which of the following reactions leads to the formation of acid rain?
A) CO₂ + H₂O → H₂CO₃
B) SO₂ + ½O₂ → SO₃; SO₃ + H₂O → H₂SO₄
C) NO₂ → NO + O
D) N₂ + O₂ → 2NO
Answer: B
Explanation: Sulfur dioxide oxidizes to sulfur trioxide, which reacts with water to form sulfuric acid (H₂SO₄), a key cause of acid rain.
Q2. The ozone layer depletion occurs mainly due to:
A) Greenhouse gases
B) CFCs releasing Cl· radicals
C) Nitrogen oxides
D) Dust particles
Answer: B
Explanation: Chlorofluorocarbons (CFCs) undergo photodissociation releasing chlorine radicals that destroy ozone molecules.
Q3. Which reaction represents photochemical smog formation?
A) NO₂ + hv → NO + O; O + O₂ → O₃
B) SO₂ + H₂O → H₂SO₃
C) N₂ + O₂ → 2NO
D) O₃ + H₂ → O₂ + H₂O
Answer: A
Explanation: NO₂ photolysis forms O atoms that combine with O₂ to generate ozone (O₃), leading to photochemical smog.
Q4. Denitrification in soil converts:
A) NO₂⁻ → NO₃⁻
B) NO₃⁻ → N₂
C) NH₃ → NO₂⁻
D) N₂ → NH₃
Answer: B
Explanation: Denitrifying bacteria reduce nitrate ions to nitrogen gas under anaerobic conditions, completing the nitrogen cycle.
Q5. Which of the following is the correct reaction for methanogenesis?
A) CO₂ + 4H₂ → CH₄ + 2H₂O
B) CH₄ + 2O₂ → CO₂ + 2H₂O
C) CO + H₂ → CH₃OH
D) C + O₂ → CO₂
Answer: A
Explanation: Methanogenic bacteria reduce carbon dioxide using hydrogen to form methane (CH₄) and water under anaerobic conditions.