Free Environmental Chemistry MCQs with Answers

11. In which of the following layers of atmosphere, is there more thickness of the ozone layer ?

• A. troposphere
• B. stratosphere
• C. mesosphere
• D. photosphere

Explanation: This layer sits above the troposphere and extends roughly from 15 to 50 kilometers above Earth's surface. It contains the majority (around 90%) of the ozone, forming the protective "ozone layer" that absorbs harmful ultraviolet (UV) radiation from the Sun.Now we'll look at why other options are incorrect.(a) Troposphere: This is the lowest layer of the atmosphere, closest to Earth's surface. Although some ozone exists here, it's formed through secondary reactions by pollutants interacting with sunlight and is harmful to our health..(c) Mesosphere: This layer above the stratosphere (50-85 km) has very little ozone present due to decreasing oxygen availability at higher altitudes.(d) Photosphere: This is not even part of Earth's atmosphere. It's the visible surface layer of the Sun where light and heat are generated.(Environmental chemistry,Components of Environment)

12. Which of the following is not a primary pollutant?

• A. SO3
• B. CO
• C. NO
• D. H2SO4

Explanation: Primary pollutants: Emitted directly into the atmosphere from a source without significant chemical alteration.Secondary pollutants: Formed in the atmosphere through chemical reactions between primary pollutants or other atmospheric constituents.Although H₂SO₄ (sulfuric acid) contributes to acid rain, sulfuric acid doesn't directly enter the atmosphere from a source. It forms in the atmosphere through complex reactions involving sulfur dioxide (SO₂), a primary pollutant from volcanic eruptions and fossil fuel combustion, with water vapor and hydroxyl radicals (OH). Therefore, it's a secondary pollutant.Now we'll look at why other options are incorrect.(a) SO₃ (sulfur trioxide): This can be considered a primary pollutant as it's directly released during the combustion of sulfur-containing fuels like coal.(b) CO (carbon monoxide): Another primary pollutant, directly emitted from incomplete combustion processes like in vehicles, industrial activities, and biomass burning.(c) NO (nitrogen oxide): Primarily originates from high-temperature combustion in vehicles, power plants, and industrial processes. Hence, it's a primary pollutant.(Environmental chemistry,Components of Environment)

13. Which of the following Air pollutants is more dangerous for the ozone layer?

• A. CFC
• B. CO2
• C. CO
• D. Oxides of Nitrogen

Explanation: WHY?Directly deplete ozone: CFCs contain chlorine and bromine atoms, which act as catalysts in the stratosphere, breaking down ozone molecules (O₃) into individual oxygen atoms (O). This significantly reduces the ozone layer's ability to filter harmful ultraviolet (UV) radiation from the sun.Long atmospheric lifetime: Once released into the atmosphere, CFCs can persist for decades or even centuries, allowing them to spread globally and exert their damaging effects on the ozone layer for prolonged periods.Montreal Protocol impact: Due to their recognized danger, CFCs were phased out globally under the Montreal Protocol, significantly contributing to the ongoing recovery of the ozone layer.Now we'll look at why other options are incorrect.(b) CO2: While a greenhouse gas, CO₂ primarily contributes to climate change. Although indirectly linked to potential long-term ozone layer impacts due to climate-driven changes, it doesn't directly deplete ozone like CFCs.(c) CO: Carbon monoxide (CO) has no significant impact on the ozone layer. Its primary concern is human and plant toxicity at ground level.(d) Oxides of Nitrogen (NOx): While NOx can participate in reactions that indirectly affect ozone levels, their impact is complex and depends on various factors like altitude and the presence of other pollutants. They are not considered direct ozone depleters like CFCs.(Environmental chemistry,Introduction and Types of Pollution Factors affecting Water Quality)

14. Which of the following factors help to measure the quality of water?

• A. DO
• B. BOD
• C. COD
• D. All of the above

Explanation: This option is correct because all three factors - DO, BOD, and COD - are important parameters used to evaluate water quality. They provide complementary information about different aspects of water pollution and its impact on aquatic environments.Now we'll look at why other options are incorrect.(a) DO (Dissolved Oxygen): Dissolved oxygen is a crucial parameter in assessing water quality. It measures the amount of oxygen dissolved in water, which is essential for the survival of aquatic organisms. Low levels of dissolved oxygen can indicate pollution or other factors affecting water quality, such as excessive organic matter decomposition.(b) BOD (Biochemical Oxygen Demand): BOD is a measure of the amount of dissolved oxygen consumed by microorganisms while decomposing organic matter in water. It provides an indication of the amount of organic pollution present in water. High BOD levels suggest high levels of organic pollutants, which can lead to oxygen depletion and harm aquatic life.(c) COD (Chemical Oxygen Demand): COD is another measure of the amount of oxygen required to chemically oxidize organic and inorganic matter in water. It provides information about the overall pollution level in water, including both biodegradable and non-biodegradable substances. High COD levels indicate high levels of pollution, which can have adverse effects on aquatic ecosystems and human health.(Environmental chemistry,Solid Waste Management and Water Treatment)

15. The main pollutant of leather tanneries in the wastewater is ?

• A. chromium III
• B. ) chromium IV
• C. ) chromium V
• D. chromium VI

Explanation: Chromium is commonly used in the tanning process of leather, and it can exist in several oxidation states. Among these states, chromium IV, also known as chromium (IV) oxide of chromium dioxide, is a particularly problematic pollutant in the wastewater from leather tanneries.(a) chromium III: Chromium III, also known as trivalent chromium, is a less toxic form of chromium compared to chromium IV. While chromium III can also be present in tannery wastewater, it is not typically considered the main pollutant. Instead, it is often used in the tanning process itself.(c) chromium V: Chromium V, also known as chromium (V) oxide or chromium trioxide, is another oxidation state of chromium. While it can be present in tannery wastewater, it is less common than chromium IV and generally less problematic in terms of pollution.(d) chromium VI: Chromium VI, also known as hexavalent chromium, is a highly toxic and carcinogenic form of chromium. It can indeed be found in tannery wastewater, but it is usually present in smaller quantities compared to chromium IV. Chromium VI is a significant concern due to its harmful effects on human health and the environment, but it is not typically considered the main pollutant in tannery wastewater.(Environmental chemistry,Introduction and Types of Pollution Factors affecting Water Quality)

16. Which substance can be used for disinfecting water?

• A. KMnO4
• B. Alums
• C. Ozone
• D. All

Explanation: As mentioned earlier, potassium permanganate is a powerful oxidizing agent and can effectively disinfect water by killing bacteria and other harmful microorganisms. It is commonly used in emergency water treatment situations and is known for its disinfectant properties. Therefore, option (a) is correct.Now we'll look at why other options are incorrect.(b) Alums:Alum, such as aluminum sulfate or potassium aluminum sulfate, is primarily used as a coagulant in water treatment processes rather than for disinfection purposes. While it can help clarify water by removing suspended particles, its main function is not as a disinfectant. Therefore, option (b) is incorrect.(c) Ozone:Ozone is indeed a potent disinfectant that can effectively kill bacteria, viruses, and other microorganisms in water. It is commonly used in water treatment plants and for purifying drinking water. Therefore, option (c) is also correct.(d) All:Option (d) states that all the substances listed can be used for disinfecting water. While this is true for KMnO4 and ozone, as explained above, alums are not primarily used as disinfectants. Therefore, option (d) is incorrect.(Environmental chemistry,Solid Waste Management and Water Treatment)

17. Which one of the following makes up the bulk of the hydrosphere's content?

• A. oceans
• B. glaciers & ice-caps
• C. ) fresh - water lakes and ponds
• D. ) All have equal distribution

Explanation: This option is correct. Oceans make up the largest portion of the Earth's hydrosphere by far, accounting for about 97% of the Earth's water. The oceans contain saltwater and cover approximately 71% of the Earth's surface.Now we'll look at why other options are incorrect.(b) Glaciers & ice-caps: While glaciers and ice caps hold a significant amount of freshwater, they do not make up the bulk of the hydrosphere's content. Glaciers and ice caps cover only a small percentage of the Earth's surface compared to the oceans.(c) Freshwater lakes and ponds: Freshwater lakes and ponds hold a smaller portion of the Earth's water compared to oceans. While they are essential sources of freshwater for many organisms and human activities, they do not constitute the majority of the hydrosphere's content.(d) All have equal distribution: This option is incorrect. The distribution of water in the hydrosphere is highly unequal. Oceans contain the vast majority of the Earth's water, followed by glaciers and ice caps, while freshwater lakes, ponds, rivers, and streams make up a relatively small percentage.(Environmental chemistry,Solid Waste Management and Water Treatment)

18. Ozone hole is substantial depletion of ozone every year during?

• A. Aug - Nov
• B. ) Sep - Nov
• C. Nov - Dec
• D. Dec - Jan

Explanation: This option is correct. The substantial depletion of the ozone layer, known as the ozone hole, occurs primarily from September to November. During these months, chemical reactions involving ozone-depleting substances, such as chlorofluorocarbons (CFCs), are most active in the polar regions, leading to significant ozone loss.Now we'll look at why other options are incorrect.a) Aug - Nov: This option is partially correct. While ozone depletion does occur during these months, it typically starts becoming substantial from September onwards, reaching its peak in October, and continuing into November. So, while August is included in the period of ozone depletion, it is not typically when substantial depletion occurs.(c) Nov - Dec: This option is incorrect. While ozone depletion may continue into December, the most substantial depletion typically occurs earlier, from September to November.(d) Dec - Jan: This option is incorrect. By December and January, ozone depletion is generally less severe compared to the peak months of September to November. While some depletion may still occur, it is not typically substantial during these months.(Environmental chemistry,Introduction and Types of Pollution Factors affecting Water Quality)

19. Which of the following is known as a quiet killer?

• A. CO2
• B. NO2
• C. CO
• D. SO2

Explanation: Carbon monoxide (CO) is known as the "silent" or "quiet killer" because it is a colorless, odorless gas that is highly toxic to humans and animals. It is produced by incomplete combustion of carbon-containing fuels such as wood, gasoline, natural gas, and coal. CO binds to hemoglobin in the blood much more readily than oxygen does, forming carboxyhemoglobin. This reduces the blood's ability to carry oxygen, leading to tissue hypoxia (oxygen deficiency) and, in severe cases, death.

20. Which one of the following is not a pollution?

• A. CO2
• B. NO2
• C. CO
• D. SO2

Explanation: While carbon dioxide is a greenhouse gas and contributes to climate change, it is not typically classified as a pollutant in the traditional sense. It is a natural component of Earth's atmosphere and is essential for photosynthesis, which is the process that plants use to produce oxygen.