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Vidaara.orgClass 11 · Chemistry
CodeVID-C11-14-CH-01
Chapter Assignment — Environmental Chemistry
Chapter: Environmental Chemistry
Topic: All Topics
Maximum Marks: 40
Time: 90 minutes
Name: ____________________ Roll No.: __________ Date: ____________

General Instructions

  • This is a full-length test covering the whole chapter — every topic is included.
  • 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 required.
Section A — Multiple Choice Questions 6 × 1 = 6 marks
1.
The ozone layer protects life by absorbing:
  • A.infrared radiation
  • B.UV-B radiation
  • C.radio waves
  • D.visible light
2.
Acid rain has a pH:
  • A.above 7
  • B.below about 5.6
  • C.exactly 7
  • D.above 8
3.
A high BOD indicates:
  • A.clean water
  • B.heavy organic pollution
  • C.high dissolved oxygen
  • D.no bacteria
4.
Green chemistry aims to:
  • A.prevent pollution at source
  • B.dilute waste
  • C.increase by-products
  • D.burn all waste
5.
DDT is a/an:
  • A.fertiliser
  • B.herbicide
  • C.insecticide
  • D.fungicide
6.
The chief greenhouse gas from human activity is:
  • A.N2
  • B.O2
  • C.CO2
  • D.Ar
Section B — Short Answer (2 marks) 4 × 2 = 8 marks
7.
Write equations to show how SO2 leads to acid rain.
8.
Define BOD and state how it relates to water quality.
9.
Why does one chlorine radical destroy many ozone molecules?
10.
Give one green-chemistry alternative to chlorine bleaching and explain why it is safer.
Section C — Short Answer (3 marks) 2 × 3 = 6 marks
11.
Compare photochemical smog and London smog (conditions, components, chemical nature).
12.
Explain eutrophication and the role of fertilisers.
Section D — Long Answer (5 marks) 2 × 5 = 10 marks
13.
Describe stratospheric ozone formation and depletion, the role of CFCs (with equations), the ozone hole, and the effects of increased UV-B on living things.
14.
Explain green chemistry and atom economy, and discuss three examples (H2O2 bleaching, solvent replacement, liquid-CO2 dry cleaning) showing how pollution is reduced.

Answer Key

Section A — Multiple Choice Questions
  1. (B) UV-B radiation
  2. (B) below about 5.6
  3. (B) heavy organic pollution
  4. (A) prevent pollution at source
  5. (C) insecticide
  6. (C) CO2
Section B — Short Answer (2 marks)
  1. 2SO2 + O2 → 2SO3; SO3 + H2O → H2SO4.
  2. BOD is the oxygen (mg/L) microbes need to decompose the organic matter in one litre of water; higher BOD means more organic pollution and poorer quality.
  3. Cl is regenerated each cycle (Cl• + O3 → ClO• + O2; ClO• + O → Cl• + O2), so it acts as a catalyst.
  4. Hydrogen peroxide; it decomposes to harmless water and oxygen, avoiding toxic organochlorine by-products.
Section C — Short Answer (3 marks)
  1. Photochemical smog: warm sunny air, from NO2 + hydrocarbons, components ozone/PAN, oxidising. London smog: cold humid air, from SO2 + soot, reducing.
  2. Nitrate/phosphate run-off from fertilisers enriches a lake, causing algal blooms; their decay consumes dissolved oxygen, killing fish — this is eutrophication.
Section D — Long Answer (5 marks)
  1. Formation: UV splits O2 → 2O, then O + O2 → O3. CFCs rise and UV releases Cl: CF2Cl2 → CF2Cl• + Cl•. Depletion: Cl• + O3 → ClO• + O2; ClO• + O → Cl• + O2 (catalytic). The ozone hole is severe seasonal thinning over Antarctica. More UV-B causes skin cancer, cataracts, weakened immunity and damage to plants and phytoplankton.
  2. Green chemistry designs processes that reduce or eliminate hazardous substances, preventing pollution at source. Atom economy is the fraction of reactant atoms ending up in the product; high atom economy means little waste. Examples: H2O2 bleaching gives only water and oxygen; replacing organic solvents with water or liquid CO2 avoids toxic emissions; dry cleaning with reusable liquid CO2 replaces the carcinogen PERC. All three cut hazardous waste and support sustainability.
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