Lesson 3.3.3.3

3.3.3.3 Ozone depletion Quiz: AQA Chemistry, Unit 3

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.3.3.3, Ozone depletion: 20 multiple choice questions for the AQA Chemistry (7405), Unit 3: Organic chemistry, written with Revision Ninja.

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The 20 questions

  1. Why is ozone in the upper atmosphere beneficial?

    • It reflects visible light into space
    • It produces oxygen for breathing
    • It makes the atmosphere warmer at ground level
    • It absorbs ultraviolet radiation

  2. What bond in CFCs is broken by ultraviolet radiation to form chlorine atoms?

    • C-F only
    • C-H
    • C-Cl
    • O-O

  3. What is the function of chlorine atoms in the decomposition of ozone?

    • They act as a reactant that forms ozone
    • They absorb all ultraviolet radiation
    • They act as a catalyst, being regenerated in the cycle
    • They are consumed completely and do not regenerate

  4. Which equation shows the first step of the chlorine catalysed decomposition of ozone?

    • ClO + O2 -> Cl + O3
    • Cl + O3 -> ClO + O2
    • Cl + O2 -> ClO2
    • O3 + O3 -> 2O2 + O2

  5. Which equation shows the second step regenerating chlorine atoms in ozone decomposition?

    • ClO + O2 -> Cl + O3
    • Cl + O2 -> ClO2
    • ClO + O3 -> 2O2 + Cl
    • ClO + ClO -> Cl2 + O2

  6. What is the overall equation for the chlorine-catalysed decomposition of ozone?

    • 2O3 -> 3O2
    • Cl2 + O3 -> ClO2 + O
    • O3 + O2 -> O4
    • O3 -> O2 + O

  7. What is the common name of the group of compounds responsible for the chlorine atoms in ozone depletion?

    • Chlorofluorocarbons (CFCs)
    • Polyalkenes
    • Alcohols
    • Carboxylic acids

  8. Why were CFCs once widely used?

    • They were strong acids used in batteries
    • They were unreactive and useful as solvents and refrigerants
    • They were ionic and used as fertilisers
    • They were highly reactive and used as fuels

  9. What has been developed to replace CFCs in their uses?

    • Alternative chlorine-free compounds
    • Radioactive materials
    • Pure chlorine gas
    • More CFCs with a higher chlorine content

  10. Which result provided evidence for legislation banning CFCs as solvents and refrigerants?

    • Research by different groups showing ozone depletion caused by chlorine atoms
    • Observations that CFCs are non-toxic and cheap to make
    • A measurement that CFCs are good fuels
    • The discovery that ozone is harmful to plants only

  11. Why is one chlorine atom able to destroy many ozone molecules?

    • It is regenerated in each cycle and so acts as a catalyst
    • It reacts with every ozone molecule at once and is then permanently used up
    • It converts ozone into chlorine gas permanently
    • It absorbs ozone into the stratosphere as a solid

  12. Which wavelength range of radiation is absorbed by ozone in the upper atmosphere?

    • Radio waves
    • Ultraviolet
    • Infrared only
    • Gamma rays only

  13. What is the 'hole in the ozone layer'?

    • A region of reduced ozone concentration in the upper atmosphere
    • A place where oxygen is produced in large amounts
    • A region where ozone is produced at ground level
    • A tear in the ground layer of the atmosphere

  14. Which equation shows that O3 decomposes to O2 and an oxygen atom?

    • O2 -> 2O
    • O3 -> O2 + O
    • O3 -> 2O2
    • O3 + O -> O4

  15. What is the oxidation state of chlorine in ClO?

    • +2
    • +1
    • -1
    • 0

  16. Which of these compounds is a chlorine-free replacement for CFCs?

    • Hydrofluorocarbons (HFCs)
    • Chloromethane
    • Dichlorodifluoromethane
    • Carbon tetrachloride

  17. Why are alkenes not the main cause of ozone depletion in the upper atmosphere?

    • Alkenes are the only compounds that absorb UV radiation
    • Alkenes produce oxygen which increases ozone
    • Ozone depletion is caused by chlorine atoms released from CFCs, not by alkenes
    • Alkenes react with ozone to form CFCs

  18. Explain why CFCs stay in the atmosphere long enough to reach the upper atmosphere.

    • CFCs react rapidly with oxygen at ground level
    • CFCs are very unreactive in the lower atmosphere, so they persist until UV radiation breaks them up higher up
    • CFCs are always solids that remain on the ground
    • CFCs dissolve completely in rain and then rise

  19. Explain why the decomposition of ozone catalysed by chlorine atoms is significant even at low chlorine concentration.

    • Chlorine atoms react only with oxygen, not ozone
    • Ozone reacts with chlorine to form a stable product that stops the cycle
    • Chlorine atoms are only present at high concentration
    • Each chlorine atom can break down many ozone molecules because it is regenerated in the cycle

  20. Explain why the legislation banning CFCs needed evidence from research.

    • The ban was needed because CFCs were found to be food additives
    • CFCs were banned because they were too cheap to produce
    • Governments need no evidence to restrict chemicals
    • Legislation needed scientific evidence showing that CFCs caused ozone depletion before governments acted

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