Air, Water, Pollution, Greenhouse Gases and Environmental Chemistry

1. Which gas makes up the largest percentage of clean dry air?

A oxygen
B nitrogen
C carbon dioxide
D argon

2. Which row gives the approximate percentages of nitrogen and oxygen in clean dry air?

	nitrogen	oxygen
A	21%	78%
B	78%	21%
C	50%	50%
D	0.04%	21%

3. Which statement about air is correct?

A Air is a compound because it contains nitrogen and oxygen.
B Air is a mixture because its gases are not chemically combined.
C Air is an element because nitrogen is the largest component.
D Air is pure because it is colourless.

4. Which gas is present in clean dry air at about 0.04%?

A oxygen
B nitrogen
C carbon dioxide
D hydrogen

5. Which gas in air is used by plants during photosynthesis?

A nitrogen
B oxygen
C carbon dioxide
D argon

6. Which gas in air is used during respiration and combustion?

A oxygen
B nitrogen
C carbon dioxide
D neon

7. Which process removes oxygen from air?

A photosynthesis
B combustion
C cracking
D thermal decomposition of limestone

8. Which process adds oxygen to air?

A respiration
B combustion
C photosynthesis
D rusting

9. Which pair of processes both increase the concentration of carbon dioxide in air?

A respiration and combustion
B photosynthesis and respiration
C photosynthesis and rusting
D neutralisation and cracking

10. Which pair of processes both decrease the concentration of carbon dioxide in air?

A combustion and respiration
B photosynthesis and dissolving in oceans
C burning fossil fuels and deforestation
D respiration and decomposition

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

11. Which pollutant is produced by incomplete combustion of carbon-containing fuels?

A carbon monoxide
B sulfur dioxide
C nitrogen
D oxygen

12. Why is carbon monoxide dangerous?

A It dissolves in rainwater to form acid rain.
B It combines with haemoglobin and reduces oxygen transport in blood.
C It reacts with oxygen to form ozone in the lungs.
D It causes eutrophication directly.

13. Which gas is mainly responsible for acid rain from burning sulfur-containing fossil fuels?

A sulfur dioxide
B carbon monoxide
C methane
D hydrogen

14. Which statement about sulfur dioxide is correct?

A It is formed by complete combustion of pure hydrogen.
B It is formed when sulfur impurities in fossil fuels burn.
C It is formed only during photosynthesis.
D It is harmless because it is naturally acidic.

15. Which pollutant is formed in car engines when nitrogen and oxygen react at high temperature?

A nitrogen dioxide
B carbon dioxide
C sulfur dioxide
D methane

16. Which pollutant causes respiratory problems and contributes to acid rain and photochemical smog?

A nitrogen oxides
B argon
C hydrogen
D water vapour

17. Which substance is used in catalytic converters to reduce nitrogen oxides?

A carbon dioxide
B carbon monoxide
C nitrogen
D sulfuric acid

18. In a catalytic converter, which pair of harmful gases can be converted into less harmful gases?

A carbon monoxide and nitrogen oxides
B oxygen and nitrogen
C argon and carbon dioxide
D water vapour and methane

19. Which products can form from carbon monoxide and nitrogen monoxide in a catalytic converter?

A carbon dioxide and nitrogen
B carbon dioxide and ammonia
C carbon monoxide and oxygen
D methane and nitrogen

20. Which equation could represent a reaction in a catalytic converter?

A 2CO + 2NO → 2CO2 + N2
B CO2 + N2 → CO + NO
C SO2 + H2O → H2SO4
D CH4 + O2 → C + 2H2O

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

21. Which gas is a greenhouse gas?

A oxygen
B nitrogen
C carbon dioxide
D argon

22. Which pair contains only greenhouse gases?

A carbon dioxide and methane
B nitrogen and oxygen
C argon and helium
D hydrogen and nitrogen

23. Which activity increases atmospheric carbon dioxide?

A planting more trees
B burning fossil fuels
C using catalytic converters
D removing sulfur from fuels

24. Which activity decreases carbon dioxide concentration in the atmosphere?

A deforestation
B burning methane
C photosynthesis
D decomposition of plants

25. Why can deforestation increase atmospheric carbon dioxide?

A Less carbon dioxide is removed by photosynthesis.
B More nitrogen is released from tree leaves.
C Trees convert oxygen into carbon monoxide.
D Deforestation removes all greenhouse gases.

26. Which statement about the greenhouse effect is correct?

A Greenhouse gases absorb infrared radiation emitted by Earth.
B Greenhouse gases prevent all sunlight from reaching Earth.
C Oxygen and nitrogen are the main greenhouse gases.
D The greenhouse effect is caused only by acid rain.

27. Which consequence is linked to enhanced greenhouse effect?

A global warming
B decreased sea level
C complete removal of oxygen
D instant freezing of oceans

28. Which gas has a significant greenhouse effect and is released by cattle and decomposition in wetlands?

A methane
B oxygen
C sulfur dioxide
D nitrogen

29. Which pollutant is most directly linked to global warming rather than acid rain?

A carbon dioxide
B sulfur dioxide
C nitrogen dioxide
D chlorine

30. Which change would reduce carbon dioxide emissions?

A burning more coal
B increasing use of renewable energy
C cutting forests for fuel
D using petrol cars more often

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

31. Which statement about water treatment is correct?

A Filtration removes all dissolved salts from water.
B Chlorination kills harmful microorganisms.
C Distillation is always used for all drinking water supplies.
D Sedimentation adds bacteria to water.

32. In water treatment, what is the purpose of filtration?

A remove insoluble solids
B kill bacteria only
C add chlorine
D remove all dissolved gases

33. In water treatment, what is the purpose of chlorination?

A remove sand
B kill bacteria and other harmful microorganisms
C remove all dissolved salts
D make water acidic

34. Which process removes insoluble solids from river water before filtration?

A sedimentation
B cracking
C electrolysis
D combustion

35. Which sample is pure water?

A river water
B seawater
C distilled water
D tap water with dissolved minerals

36. Why is seawater not suitable for drinking without treatment?

A It contains dissolved salts at high concentration.
B It contains no water molecules.
C It is an element.
D It contains only oxygen and hydrogen gases.

37. Which process can obtain pure water from seawater?

A filtration only
B crystallisation only
C simple distillation
D paper chromatography

38. Which statement about potable water is correct?

A It must be chemically pure water only.
B It is water safe to drink, even if it contains small amounts of dissolved substances.
C It must contain no dissolved oxygen.
D It is made by electrolysis of hydrogen.

39. Which ion in water causes temporary hardness?

A Ca2+
B Na+
C K+
D NH4+

40. Temporary hardness in water can be removed by boiling because it contains dissolved:

A calcium hydrogencarbonate
B sodium chloride
C potassium nitrate
D magnesium sulfate only

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

41. Which equation shows the formation of limescale from temporary hard water?

A Ca(HCO3)2 → CaCO3 + CO2 + H2O
B CaCO3 → CaO + CO2
C CaCl2 + Na2CO3 → CaCO3 + 2NaCl
D CaO + H2O → Ca(OH)2

42. Which statement about hard water is correct?

A It forms scum with soap.
B It always contains only sodium ions.
C It is always poisonous.
D It cannot be softened by any method.

43. Which substance can soften hard water by precipitating calcium ions?

A sodium carbonate
B sodium chloride
C hydrochloric acid
D ethanol

44. Which problem is caused by hard water in kettles and boilers?

A formation of limescale
B formation of chlorine gas
C removal of all dissolved oxygen
D production of carbon monoxide

45. Which advantage can hard water have?

A It can provide calcium ions for health.
B It contains no dissolved substances.
C It prevents soap scum completely.
D It always has pH 14.

46. Which pollutant causes eutrophication when present in excess in water?

A nitrates from fertilisers
B oxygen from photosynthesis
C argon from air
D copper metal pieces

47. What is the correct sequence in eutrophication?

A nitrates increase → algae grow rapidly → bacteria decompose dead algae → oxygen decreases
B oxygen increases → fish reproduce rapidly → algae disappear → nitrates decrease
C sulfur dioxide dissolves → pH increases → fish grow faster
D carbon monoxide dissolves → water becomes pure

48. Which substance is most likely to cause acid rain?

A sulfur dioxide
B methane
C argon
D calcium carbonate

49. Which effect is caused by acid rain?

A increased pH of lakes
B corrosion of limestone buildings
C formation of oxygen from nitrogen
D removal of all greenhouse gases

50. Which row correctly matches pollutant and effect?

	pollutant	effect
A	carbon monoxide	reduces oxygen transport in blood
B	sulfur dioxide	causes eutrophication only
C	methane	causes acid rain directly
D	nitrates	relight glowing splint

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

1. B

A wrong: Oxygen is about 21%.
B right: Nitrogen is the largest part of clean dry air, about 78%.
C wrong: Carbon dioxide is only about 0.04%.
D wrong: Argon is about 1%.

2. B

A wrong: Reversed.
B right: Clean dry air is about 78% nitrogen and 21% oxygen.
C wrong: Not equal amounts.
D wrong: 0.04% is carbon dioxide, not nitrogen.

3. B

A wrong: Nitrogen and oxygen are not chemically combined in air.
B right: Air is a mixture of gases.
C wrong: Air contains several substances, so it is not an element.
D wrong: Colourless does not mean pure.

4. C

A wrong: Oxygen is about 21%.
B wrong: Nitrogen is about 78%.
C right: Carbon dioxide is about 0.04% in clean dry air.
D wrong: Hydrogen is present only in tiny traces.

5. C

A wrong: Nitrogen is not directly used in photosynthesis.
B wrong: Oxygen is produced during photosynthesis.
C right: Plants use carbon dioxide during photosynthesis.
D wrong: Argon is unreactive and not used.

6. A

A right: Oxygen is used in respiration and combustion.
B wrong: Nitrogen is mostly unreactive.
C wrong: Carbon dioxide is a product of respiration and combustion.
D wrong: Neon is a noble gas.

7. B

A wrong: Photosynthesis adds oxygen.
B right: Combustion uses oxygen.
C wrong: Cracking does not mainly remove oxygen from air.
D wrong: Thermal decomposition of limestone releases carbon dioxide, not oxygen.

8. C

A wrong: Respiration uses oxygen.
B wrong: Combustion uses oxygen.
C right: Photosynthesis releases oxygen.
D wrong: Rusting uses oxygen.

9. A

A right: Respiration and combustion both release carbon dioxide.
B wrong: Photosynthesis removes carbon dioxide.
C wrong: Photosynthesis removes carbon dioxide and rusting mainly uses oxygen.
D wrong: Neutralisation and cracking are not main CO2-raising air processes.

10. B

A wrong: Both increase carbon dioxide.
B right: Photosynthesis removes CO2; oceans dissolve some CO2.
C wrong: Both increase atmospheric CO2.
D wrong: Both usually increase CO2.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

11. A

A right: Incomplete combustion produces carbon monoxide.
B wrong: Sulfur dioxide comes from burning sulfur impurities.
C wrong: Nitrogen is not a pollutant from incomplete combustion.
D wrong: Oxygen is a reactant.

12. B

A wrong: Acid rain is mainly linked to SO2 and NOx.
B right: Carbon monoxide binds to haemoglobin, reducing oxygen transport.
C wrong: This is not the main danger.
D wrong: Eutrophication is caused by excess nitrates/phosphates.

13. A

A right: Burning sulfur-containing fuels produces sulfur dioxide, which causes acid rain.
B wrong: Carbon monoxide is toxic but not acid rain’s main cause.
C wrong: Methane is a greenhouse gas.
D wrong: Hydrogen is not responsible.

14. B

A wrong: Pure hydrogen burns to form water.
B right: Sulfur dioxide forms when sulfur impurities in fossil fuels burn.
C wrong: Photosynthesis does not form SO2.
D wrong: It is harmful and acidic.

15. A

A right: At high engine temperatures, nitrogen and oxygen react to form nitrogen oxides such as nitrogen dioxide.
B wrong: Carbon dioxide comes from combustion of carbon fuels.
C wrong: Sulfur dioxide comes from sulfur impurities.
D wrong: Methane is a fuel/greenhouse gas.

16. A

A right: Nitrogen oxides cause respiratory problems and contribute to acid rain and photochemical smog.
B wrong: Argon is unreactive.
C wrong: Hydrogen is not this pollutant.
D wrong: Water vapour is not the named pollutant here.

17. B

A wrong: Carbon dioxide is a product, not the reducing substance.
B right: Carbon monoxide helps reduce nitrogen oxides to nitrogen in catalytic converters.
C wrong: Nitrogen is a product.
D wrong: Sulfuric acid is unrelated.

18. A

A right: Catalytic converters convert carbon monoxide and nitrogen oxides into less harmful gases.
B wrong: Oxygen and nitrogen are already not the harmful exhaust gases here.
C wrong: Argon is not involved.
D wrong: Water vapour and methane are not the main pair.

19. A

A right: Carbon monoxide and nitrogen monoxide can form carbon dioxide and nitrogen.
B wrong: Ammonia is not the product here.
C wrong: That would not make pollutants less harmful.
D wrong: Methane is not formed.

20. A

A right: 2CO + 2NO → 2CO2 + N2 is a catalytic converter reaction.
B wrong: Reverse of the useful change.
C wrong: This relates to acid rain/sulfuric acid formation, not catalytic converters.
D wrong: This is incomplete combustion of methane.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

21. C

A wrong: Oxygen is not a major greenhouse gas at this level.
B wrong: Nitrogen is not a greenhouse gas.
C right: Carbon dioxide is a greenhouse gas.
D wrong: Argon is not a greenhouse gas.

22. A

A right: Carbon dioxide and methane are both greenhouse gases.
B wrong: Nitrogen and oxygen are not the key greenhouse gases.
C wrong: Argon and helium are not greenhouse gases.
D wrong: Hydrogen and nitrogen are not greenhouse gases.

23. B

A wrong: Planting trees removes carbon dioxide by photosynthesis.
B right: Burning fossil fuels releases carbon dioxide.
C wrong: Catalytic converters reduce some pollutants, not mainly increase CO2 as the intended answer.
D wrong: Removing sulfur reduces SO2, not CO2.

24. C

A wrong: Deforestation increases CO2.
B wrong: Burning methane produces CO2.
C right: Photosynthesis removes carbon dioxide from air.
D wrong: Decomposition releases carbon dioxide/methane.

25. A

A right: Fewer trees means less carbon dioxide is removed by photosynthesis.
B wrong: Nitrogen release is not the key reason.
C wrong: Trees do not convert oxygen into carbon monoxide.
D wrong: Deforestation does not remove greenhouse gases.

26. A

A right: Greenhouse gases absorb infrared radiation emitted by Earth.
B wrong: They do not block all sunlight.
C wrong: Oxygen and nitrogen are not the main greenhouse gases.
D wrong: Acid rain is separate.

27. A

A right: Enhanced greenhouse effect is linked to global warming.
B wrong: Sea level can rise, not decrease.
C wrong: Oxygen is not completely removed.
D wrong: Oceans do not instantly freeze.

28. A

A right: Methane is released by cattle and wetlands and has a strong greenhouse effect.
B wrong: Oxygen is not the gas.
C wrong: Sulfur dioxide is linked more to acid rain.
D wrong: Nitrogen is not a greenhouse gas.

29. A

A right: Carbon dioxide is directly linked to global warming.
B wrong: Sulfur dioxide is mainly linked to acid rain.
C wrong: Nitrogen dioxide is mainly acid rain/smog.
D wrong: Chlorine is not the main global-warming gas here.

30. B

A wrong: Burning more coal increases CO2.
B right: Renewable energy can reduce fossil fuel burning and CO2 emissions.
C wrong: Cutting forests increases CO2.
D wrong: Petrol cars increase CO2 emissions.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

31. B

A wrong: Filtration removes insoluble solids, not all dissolved salts.
B right: Chlorination kills harmful microorganisms.
C wrong: Distillation is not always used for drinking water.
D wrong: Sedimentation helps remove solids; it does not add bacteria.

32. A

A right: Filtration removes insoluble solids.
B wrong: Killing bacteria is chlorination.
C wrong: Adding chlorine is chlorination.
D wrong: Filtration does not remove all dissolved gases.

33. B

A wrong: Sand is removed by sedimentation/filtration.
B right: Chlorination kills bacteria and harmful microorganisms.
C wrong: It does not remove all dissolved salts.
D wrong: It is not done to make water acidic.

34. A

A right: Sedimentation allows suspended insoluble solids to settle before filtration.
B wrong: Cracking is hydrocarbon decomposition.
C wrong: Electrolysis decomposes substances using electricity.
D wrong: Combustion is burning.

35. C

A wrong: River water contains dissolved and suspended substances.
B wrong: Seawater contains dissolved salts.
C right: Distilled water is pure water.
D wrong: Tap water contains dissolved minerals.

36. A

A right: Seawater has high concentration of dissolved salts.
B wrong: It contains water molecules.
C wrong: It is a mixture, not an element.
D wrong: It is not oxygen and hydrogen gases.

37. C

A wrong: Filtration cannot remove dissolved salts.
B wrong: Crystallisation obtains salt, not pure water.
C right: Simple distillation evaporates and condenses water, leaving salts behind.
D wrong: Chromatography is not used for bulk water purification.

38. B

A wrong: Potable water does not have to be chemically pure.
B right: Potable water is safe to drink and may contain small amounts of dissolved substances.
C wrong: It can contain dissolved oxygen.
D wrong: It is not made by electrolysis of hydrogen.

39. A

A right: Calcium ions cause water hardness.
B wrong: Sodium ions do not cause hardness.
C wrong: Potassium ions do not cause hardness.
D wrong: Ammonium ions do not cause hardness.

40. A

A right: Temporary hardness is caused by dissolved calcium/magnesium hydrogencarbonates; boiling decomposes them.
B wrong: Sodium chloride does not cause temporary hardness.
C wrong: Potassium nitrate does not cause temporary hardness.
D wrong: Magnesium sulfate causes permanent hardness, not temporary hardness.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

41. A

A right: Calcium hydrogencarbonate decomposes on boiling to form calcium carbonate limescale, carbon dioxide and water.
B wrong: This is thermal decomposition of calcium carbonate.
C wrong: This is precipitation of calcium carbonate using sodium carbonate.
D wrong: This is slaking lime.

42. A

A right: Hard water forms scum with soap.
B wrong: Hard water contains calcium/magnesium ions, not only sodium ions.
C wrong: Hard water is not always poisonous.
D wrong: It can be softened.

43. A

A right: Sodium carbonate precipitates calcium ions as calcium carbonate.
B wrong: Sodium chloride does not soften hard water.
C wrong: Hydrochloric acid is not used to soften drinking water.
D wrong: Ethanol does not remove Ca2+.

44. A

A right: Hard water forms limescale in kettles and boilers.
B wrong: Chlorine gas is not formed.
C wrong: It does not remove all dissolved oxygen.
D wrong: Carbon monoxide is not produced.

45. A

A right: Hard water can provide calcium ions, which may be beneficial.
B wrong: Hard water contains dissolved substances.
C wrong: It forms soap scum.
D wrong: It is not always pH 14.

46. A

A right: Excess nitrates from fertilisers cause eutrophication.
B wrong: Oxygen does not cause eutrophication.
C wrong: Argon is unreactive.
D wrong: Copper metal pieces are not the usual cause.

47. A

A right: Nitrates increase → algal bloom → dead algae decomposed by bacteria → oxygen decreases.
B wrong: Oxygen does not increase overall; it decreases after decomposition.
C wrong: Acid rain lowers pH, not eutrophication.
D wrong: Carbon monoxide does not purify water.

48. A

A right: Sulfur dioxide dissolves/reacts in rainwater to form acidic solutions.
B wrong: Methane is a greenhouse gas.
C wrong: Argon is unreactive.
D wrong: Calcium carbonate neutralises acids.

49. B

A wrong: Acid rain decreases pH of lakes.
B right: Acid rain corrodes limestone buildings.
C wrong: It does not form oxygen from nitrogen.
D wrong: It does not remove greenhouse gases.

50. A

A right: Carbon monoxide reduces oxygen transport in blood.
B wrong: Sulfur dioxide causes acid rain, not eutrophication only.
C wrong: Methane is a greenhouse gas, not a direct acid rain gas.
D wrong: Nitrates cause eutrophication; oxygen relights a glowing splint.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.