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Vidaara.orgClass 11 · Chemistry
CodeVID-C11-14-T1-01
Assignment — Atmospheric Pollution
Chapter: Environmental Chemistry
Topic: Atmospheric Pollution
Maximum Marks: 30
Time: 60 minutes
Name: ____________________ Roll No.: __________ Date: ____________

General Instructions

  • All questions are compulsory.
  • Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
  • Write balanced equations where asked. Only final answers are given at the end — for full solutions, raise your doubts with your teacher.
Section A — Multiple Choice Questions 5 × 1 = 5 marks
1.
The protective ozone layer is found in the:
  • A.troposphere
  • B.stratosphere
  • C.mesosphere
  • D.thermosphere
2.
Acid rain has a pH that is:
  • A.above 7
  • B.exactly 7
  • C.below about 5.6
  • D.always above 5.6
3.
Which pair of acids is mainly responsible for acid rain?
  • A.HCl and HNO3
  • B.H2SO4 and HNO3
  • C.H2CO3 and HCl
  • D.H3PO4 and HF
4.
A key oxidant present in photochemical smog is:
  • A.SO2
  • B.CO
  • C.PAN (peroxyacetyl nitrate)
  • D.N2
5.
Excess UV-B reaching the Earth due to ozone depletion can cause:
  • A.increased rainfall
  • B.skin cancer and cataracts
  • C.more oxygen in air
  • D.lower temperatures
Section B — Short Answer (2 marks) 3 × 2 = 6 marks
6.
Differentiate between a pollutant and a contaminant with one example each.
7.
Write the equations showing the formation of sulphuric acid in acid rain from SO2.
8.
Why does one chlorine radical destroy many ozone molecules?
Section C — Short Answer (3 marks) 2 × 3 = 6 marks
9.
Compare photochemical smog and classical (London) smog in terms of conditions of formation, chief components and chemical nature.
10.
Explain the greenhouse effect and name three greenhouse gases.
Section D — Long Answer (5 marks) 1 × 5 = 5 marks
11.
Describe the formation and depletion of stratospheric ozone, the role of CFCs (with equations), the meaning of the 'ozone hole', and the effects of ozone depletion on living things.

Answer Key

Section A — Multiple Choice Questions
  1. (B) stratosphere
  2. (C) below about 5.6
  3. (B) H2SO4 and HNO3
  4. (C) PAN (peroxyacetyl nitrate)
  5. (B) skin cancer and cataracts
Section B — Short Answer (2 marks)
  1. A pollutant is a substance present at a harmful concentration (e.g. SO2); a contaminant is a substance introduced into the environment by human activity that is not naturally present (e.g. a synthetic pesticide).
  2. 2SO2 + O2 → 2SO3; SO3 + H2O → H2SO4.
  3. Cl• is regenerated in the cycle (Cl• + O3 → ClO• + O2; ClO• + O → Cl• + O2), so it behaves as a catalyst and repeats the reaction thousands of times.
Section C — Short Answer (3 marks)
  1. Photochemical smog forms in warm, sunny, traffic-heavy air from NO2 + hydrocarbons; its chief components are ozone and PAN; it is oxidising. London smog forms in cold, humid air from SO2 + soot; it is reducing.
  2. Greenhouse gases let sunlight in but absorb the infrared radiation re-emitted by Earth, trapping heat in the lower atmosphere and warming it. Three examples: CO2, CH4 and water vapour (others: O3, CFCs).
Section D — Long Answer (5 marks)
  1. Formation: UV splits O2 → 2O, then O + O2 → O3, balanced by natural breakdown. CFCs rise to the stratosphere and UV releases Cl radicals: CF2Cl2 → CF2Cl• + Cl•. Depletion: Cl• + O3 → ClO• + O2; ClO• + O → Cl• + O2 (Cl regenerated, catalytic). The ozone hole is the severe seasonal thinning of ozone over Antarctica. Effects: more UV-B reaches the surface, causing skin cancer, cataracts, weakened immunity, and damage to plants and phytoplankton.
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