Environmental Chemistry – 40 MCQs Practice

Environmental Chemistry – 40 MCQs

This section provides 40 multiple-choice questions covering key concepts from Environmental Chemistry, essential for your NEET and JEE Main preparation. Each question has four options, with only one correct answer.

Section 1: Multiple Choice Questions (MCQs)

Instructions: Choose the single best answer for each question.

  1. Which of the following is a component of classical smog? A) Ozone (O3) B) Peroxyacetyl Nitrate (PAN) C) Sulfur Dioxide (SO2) D) Formaldehyde (HCHO)
  2. The gas that binds to hemoglobin much more strongly than oxygen, forming carboxyhemoglobin, is: A) Carbon dioxide (CO2) B) Carbon monoxide (CO) C) Sulfur dioxide (SO2) D) Nitrogen dioxide (NO2)
  3. Acid rain has a pH less than: A) 7.0 B) 6.5 C) 5.6 D) 4.0
  4. Which of the following contributes to the formation of photochemical smog? A) SO2 and H2S B) NOx and unsaturated hydrocarbons C) CO2 and CH4 D) CFCs and O3
  5. The major components of photochemical smog include: A) Smoke, fog, SO2 B) O3, PAN, Acrolein C) CO, CO2, H2S D) H2SO4, HNO3
  6. Which layer of the atmosphere contains the ozone layer? A) Troposphere B) Stratosphere C) Mesosphere D) Thermosphere
  7. The depletion of the ozone layer is primarily caused by: A) Carbon dioxide B) Methane C) Chlorofluorocarbons (CFCs) D) Sulfur dioxide
  8. The reaction Cl⋅(g)+O3(g)→ClO⋅(g)+O2(g) represents a step in the mechanism of: A) Acid rain formation B) Photochemical smog formation C) Ozone layer depletion D) Greenhouse effect
  9. Which of the following is NOT a consequence of increased UV radiation due to ozone depletion? A) Skin cancer B) Cataracts C) Reduced crop yields D) Minamata disease
  10. The phenomenon where a body of water becomes overly enriched with nutrients, leading to excessive growth of algae, is known as: A) Biomagnification B) Eutrophication C) Cultural eutrophication D) Algal bloom (specific effect, not the overall process)
  11. Biochemical Oxygen Demand (BOD) is a measure of: A) Amount of oxygen present in water. B) Amount of oxygen consumed by microorganisms for decomposing organic matter. C) Amount of oxygen required for fish survival. D) Amount of dissolved oxygen available for respiration.
  12. A water sample with a BOD value of 20 ppm is likely to be: A) Very clean B) Moderately clean C) Highly polluted D) Safe for drinking
  13. Which of the following diseases is associated with mercury pollution? A) Itai-Itai disease B) Minamata disease C) Typhoid D) Dysentery
  14. Cadmium pollution is associated with: A) Minamata disease B) Itai-Itai disease C) Blue baby syndrome D) Fluorosis
  15. Polychlorinated Biphenyls (PCBs) are hazardous chemical pollutants because they are: A) Biodegradable B) Highly volatile C) Carcinogenic and endocrine disruptors D) Easily removed from the environment
  16. The major contributor to the greenhouse effect among the following is: A) Methane (CH4) B) Nitrous Oxide (N2O) C) Chlorofluorocarbons (CFCs) D) Carbon Dioxide (CO2)
  17. Which of the following is NOT a consequence of global warming? A) Rising sea levels B) Increased biodiversity C) More extreme weather events D) Impact on agriculture
  18. What is the primary cause of acid rain? A) CO2 emissions B) SOx and NOx emissions C) CFC emissions D) Methane emissions
  19. The corrosion of marble monuments like the Taj Mahal is an effect of: A) Photochemical smog B) Acid rain C) Ozone depletion D) Global warming
  20. Which of the following methods is a “Green Chemistry” approach to bleaching paper? A) Using Chlorine (Cl2) B) Using Hydrogen Peroxide (H2O2) C) Using Sulfur Dioxide (SO2) D) Using Hypochlorite (ClO-)
  21. The principle of Green Chemistry that aims to maximize the incorporation of all materials used in the process into the final product is: A) Prevention B) Atom Economy C) Less Hazardous Chemical Syntheses D) Design for Degradation
  22. Which of the following is an example of a viable particulate pollutant? A) Dust B) Fumes C) Pollen D) Smoke
  23. The permissible level of a pollutant in the atmosphere to which a worker is exposed in an 8-hour day without adverse effects is called: A) Permissible Exposure Limit (PEL) B) Threshold Limit Value (TLV) C) Maximum Contaminant Level (MCL) D) Lethal Dose (LD50)
  24. Which of the following pollutants is a cause of chlorosis and necrosis in plants? A) Carbon monoxide B) Sulfur dioxide C) Methane D) Carbon dioxide
  25. A chemical agent that causes genetic defects or mutations is called a: A) Carcinogen B) Teratogen C) Mutagen D) Neurotoxin
  26. The layer of the atmosphere where most of the weather phenomena occur is the: A) Stratosphere B) Troposphere C) Mesosphere D) Thermosphere
  27. Which of the following is a reducing smog? A) Classical smog B) Photochemical smog C) Los Angeles smog D) Summer smog
  28. Photochemical smog typically occurs in: A) Cool, humid climate B) Warm, dry, sunny climate C) Industrial areas with high SO2 D) Areas with high water vapor
  29. The formation of Ozone (O3) in the stratosphere is a natural process, but its presence as a pollutant in the troposphere (ground-level ozone) is harmful because it is a component of: A) Acid rain B) Classical smog C) Photochemical smog D) Ozone hole
  30. The decomposition of organic matter in water bodies by microorganisms leads to a decrease in: A) BOD B) Dissolved Oxygen (DO) C) Temperature D) Acidity
  31. Which of the following pesticides is non-biodegradable and persistent in the environment? A) Malathion B) DDT C) Carbaryl D) Pyrethrins
  32. The process of soil erosion is directly promoted by: A) Afforestation B) Sustainable agricultural practices C) Deforestation D) Bioremediation
  33. Which of the following greenhouse gases is produced from the digestion of livestock and decomposition in landfills? A) CO2 B) N2O C) CH4 D) CFCs
  34. The main reason for the decreasing pH of ocean waters (ocean acidification) is the increase in atmospheric: A) SO2 B) NOx C) CO2 D) CH4
  35. The term “Atom Economy” in Green Chemistry aims to: A) Use expensive catalysts. B) Maximize waste generation. C) Incorporate most atoms of reactants into the final product. D) Design processes that consume more energy.
  36. Which of the following is a consequence of thermal pollution in water bodies? A) Increase in dissolved oxygen. B) Decrease in dissolved oxygen. C) Increased aquatic biodiversity. D) Enhanced purification.
  37. The phenomenon of biomagnification refers to: A) Increase in size of organisms due to pollution. B) Accumulation of non-biodegradable pollutants in the food chain at increasing concentrations. C) The increase in global temperature. D) The spreading of pollutants over a large area.
  38. The principle of “Design for Degradation” in Green Chemistry suggests that chemical products should: A) Be highly persistent in the environment. B) Break down into innocuous products after their function. C) Be recycled indefinitely. D) Be incinerated after use.
  39. The depletion of stratospheric ozone layer may result in: A) Increase in infrared radiations reaching the earth. B) Increase in ultraviolet radiations reaching the earth. C) Decrease in global temperature. D) Increase in crop productivity.
  40. Which of the following is considered a primary pollutant in tropospheric air? A) PAN B) Ozone (O3) C) Carbon Monoxide (CO) D) Aldehydes

Section 2: Answer Key

  1. C
  2. B
  3. C
  4. B
  5. B
  6. B
  7. C
  8. C
  9. D
  10. B
  11. B
  12. C
  13. B
  14. B
  15. C
  16. D
  17. B
  18. B
  19. B
  20. B
  21. B
  22. C
  23. B
  24. B
  25. C
  26. B
  27. A
  28. B
  29. C
  30. B
  31. B
  32. C
  33. C
  34. C
  35. C
  36. B
  37. B
  38. B
  39. B
  40. C

Section 3: Detailed Explanations

  1. C) Sulfur Dioxide (SO2)
    • Explanation: Classical (London/Sulfurous) smog is a mixture of smoke, fog, and sulfur dioxide. Ozone, PAN, and formaldehyde are components of photochemical smog.
  2. B) Carbon monoxide (CO)
    • Explanation: Carbon monoxide is highly poisonous because it has a much higher affinity (200-300 times) for hemoglobin than oxygen, forming stable carboxyhemoglobin and impairing oxygen transport.
  3. C) 5.6
    • Explanation: Normal rainwater has a pH of approximately 5.6 due to dissolved atmospheric CO2 forming carbonic acid. Acid rain is defined as rainwater with a pH less than 5.6, primarily due to SOx and NOx.
  4. B) NOx and unsaturated hydrocarbons
    • Explanation: Photochemical smog (Los Angeles smog) is formed by the reaction of nitrogen oxides (NOx) and unsaturated hydrocarbons (volatile organic compounds, VOCs) in the presence of sunlight.
  5. B) O3, PAN, Acrolein
    • Explanation: Photochemical smog is characterized by the presence of strong oxidizing agents like Ozone (O3), Peroxyacetyl Nitrate (PAN), and aldehydes like Acrolein and Formaldehyde. Smoke, fog, and SO2 are associated with classical smog.
  6. B) Stratosphere
    • Explanation: The ozone layer, which protects Earth from harmful UV radiation, is located in the stratosphere, approximately 10-50 km above sea level.
  7. C) Chlorofluorocarbons (CFCs)
    • Explanation: CFCs (Freons) are the most significant ozone-depleting substances. They release chlorine free radicals in the stratosphere, which catalytically destroy ozone.
  8. C) Ozone layer depletion
    • Explanation: This reaction shows a chlorine radical (Cl·) reacting with an ozone molecule (O3) to form chlorine monoxide radical (ClO·) and molecular oxygen (O2). This is a key propagation step in the catalytic destruction of ozone by CFCs.
  9. D) Minamata disease
    • Explanation: Minamata disease is caused by mercury pollution. Skin cancer, cataracts, and reduced crop yields are direct consequences of increased UV radiation reaching Earth due to ozone depletion.
  10. B) Eutrophication
    • Explanation: Eutrophication is the process of nutrient enrichment in water bodies, leading to excessive algal growth (algal bloom), which consumes dissolved oxygen upon decomposition, harming aquatic life.
  11. B) Amount of oxygen consumed by microorganisms for decomposing organic matter.
    • Explanation: Biochemical Oxygen Demand (BOD) is a measure of the amount of dissolved oxygen consumed by aerobic microorganisms when decomposing organic matter in a water sample over a specific period (usually 5 days at 20°C). High BOD indicates high organic pollution.
  12. C) Highly polluted
    • Explanation: Water with a BOD value less than 5 ppm is considered clean. A BOD value greater than 17 ppm indicates highly polluted water. 20 ppm falls into the highly polluted category.
  13. B) Minamata disease
    • Explanation: Minamata disease is a neurological syndrome caused by severe mercury poisoning, which was first identified in Minamata, Japan, due to industrial wastewater contaminated with methylmercury.
  14. B) Itai-Itai disease
    • Explanation: Itai-Itai disease (ouch-ouch disease) is a painful bone and joint disorder caused by severe cadmium poisoning.
  15. C) Carcinogenic and endocrine disruptors
    • Explanation: Polychlorinated Biphenyls (PCBs) are persistent organic pollutants (POPs) that are highly toxic, non-biodegradable, and can cause cancer, reproductive problems, and disrupt endocrine systems.
  16. D) Carbon Dioxide (CO2)
    • Explanation: While all listed are greenhouse gases, carbon dioxide is the largest contributor to the enhanced greenhouse effect and global warming due to its high concentration and emission from fossil fuel combustion and deforestation.
  17. B) Increased biodiversity
    • Explanation: Global warming is linked to adverse environmental changes, including habitat loss and species extinction, leading to decreased biodiversity, not increased. Rising sea levels, extreme weather, and agricultural impacts are all consequences.
  18. B) SOx and NOx emissions
    • Explanation: Acid rain is primarily caused by sulfur dioxide (SO2) and oxides of nitrogen (NOx) released from burning fossil fuels, which react with water vapor to form sulfuric acid and nitric acid.
  19. B) Acid rain
    • Explanation: Acid rain corrodes limestone and marble monuments like the Taj Mahal through reactions such as CaCO3 + H2SO4 -> CaSO4 + H2O + CO2.
  20. B) Using Hydrogen Peroxide (H2O2)
    • Explanation: Green Chemistry promotes the use of less hazardous chemicals. Replacing chlorine gas (Cl2) with hydrogen peroxide (H2O2) for bleaching paper is a green chemistry practice as H2O2 is a cleaner oxidizing agent, decomposing to water and oxygen.
  21. B) Atom Economy
    • Explanation: Atom economy is a key principle of Green Chemistry that focuses on maximizing the incorporation of all atoms from the reactants into the desired product, thereby minimizing waste.
  22. C) Pollen
    • Explanation: Viable particulates are living organisms or spores like bacteria, fungi, moulds, and pollen, which can cause allergies and diseases. Dust, fumes, and smoke are non-viable particulates.
  23. B) Threshold Limit Value (TLV)
    • Explanation: The Threshold Limit Value (TLV) is the maximum concentration of a chemical or physical agent to which a worker can be exposed day after day without adverse health effects over an 8-hour workday.
  24. B) Sulfur dioxide
    • Explanation: Sulfur dioxide (SO2) is a major air pollutant that causes chlorosis (yellowing of leaves due to chlorophyll loss) and necrosis (death of tissue, appearing as brown spots) in plants.
  25. C) Mutagen
    • Explanation: A mutagen is a chemical or physical agent that can cause changes in the genetic material (DNA), leading to mutations. Carcinogens cause cancer, and teratogens cause birth defects.
  26. B) Troposphere
    • Explanation: The troposphere is the lowest layer of Earth’s atmosphere, extending up to about 10 km from sea level, where most weather phenomena occur.
  27. A) Classical smog
    • Explanation: Classical smog (London smog or sulfurous smog) is reducing in nature because it primarily consists of sulfur dioxide (SO2), which acts as a reducing agent. Photochemical smog is oxidizing.
  28. B) Warm, dry, sunny climate
    • Explanation: Photochemical smog (Los Angeles smog) forms readily in warm, dry, and sunny conditions, as sunlight is essential for the chemical reactions involving NOx and hydrocarbons.
  29. C) Photochemical smog
    • Explanation: While stratospheric ozone is beneficial, ground-level ozone (tropospheric ozone) is a harmful secondary pollutant formed as a key component of photochemical smog.
  30. B) Dissolved Oxygen (DO)
    • Explanation: The decomposition of organic matter by microorganisms in water bodies is an aerobic process that consumes dissolved oxygen. A high organic load leads to high BOD and consequently, a significant decrease in dissolved oxygen (DO), which can harm aquatic life.
  31. B) DDT
    • Explanation: DDT (Dichlorodiphenyltrichloroethane) is a persistent organic pollutant (POP). It is non-biodegradable and accumulates in the environment and food chains (biomagnification).
  32. C) Deforestation
    • Explanation: Deforestation removes tree cover, which protects the soil from the erosive forces of wind and rain. This directly promotes soil erosion.
  33. C) CH4
    • Explanation: Methane (CH4) is a potent greenhouse gas produced naturally and anthropogenically, largely from the anaerobic decomposition of organic matter in landfills and the digestion processes of livestock (ruminants).
  34. C) CO2
    • Explanation: Ocean acidification is primarily caused by the absorption of excess atmospheric carbon dioxide (CO2) by the oceans. CO2 reacts with water to form carbonic acid (H2CO3), which then dissociates, increasing the acidity of seawater.
  35. C) Incorporate most atoms of reactants into the final product.
    • Explanation: Atom economy aims to maximize the efficiency of chemical reactions by ensuring that as many atoms from the starting materials as possible are incorporated into the desired final product, thereby minimizing waste.
  36. B) Decrease in dissolved oxygen.
    • Explanation: Thermal pollution involves the discharge of hot water into water bodies. Increased water temperature reduces the solubility of dissolved gases, including oxygen. A decrease in dissolved oxygen harms aquatic life.
  37. B) Accumulation of non-biodegradable pollutants in the food chain at increasing concentrations.
    • Explanation: Biomagnification (or bioamplification) is the increasing concentration of a substance, such as a toxic chemical (e.g., DDT, mercury), in the tissues of organisms at successively higher trophic levels in a food chain. This happens because the pollutants are non-biodegradable and accumulate.
  38. B) Break down into innocuous products after their function.
    • Explanation: The principle of “Design for Degradation” in Green Chemistry encourages the design of chemical products that, after fulfilling their function, degrade into non-toxic substances and do not persist in the environment.
  39. B) Increase in ultraviolet radiations reaching the earth.
    • Explanation: The stratospheric ozone layer absorbs harmful ultraviolet (UV) radiation from the sun. Its depletion leads to an increase in UV radiation reaching the Earth’s surface, which can cause skin cancer, cataracts, and other adverse effects.
  40. C) Carbon Monoxide (CO)
    • Explanation: Primary pollutants are those emitted directly from a source into the atmosphere. Carbon monoxide is directly emitted from incomplete combustion. PAN and tropospheric ozone are secondary pollutants, formed by reactions of primary pollutants in the atmosphere. Aldehydes can be both primary and secondary.

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