What does ${\rm{BO}}{{\rm{D}}_5}$ represent?

Biological ozone depletion in five days

Dissolved oxygen left after five days

Micro-organisms killed by ozone in sewage treatment plants in five hours

ENVIRONMENTAL CHEMISTRY MCQs for NEET UG CHEMISTRY — Easy

1 Easy

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Understanding +4 | -1

Increasing skin cancer and high mutation rate are due to

View answer and explanation

Correct option: B

Ozone depletion

Option B (Ozone depletion) is correct because ozone depletion leads to increased UV radiation reaching the Earth's surface, causing skin cancer and mutations.

Solution approach

Correct Answer + Core Reason: Ozone depletion. Increased UV radiation due to ozone depletion causes skin cancer and mutations.

Step-by-Step Solution:
Step 1: Understand the function of the ozone layer in the stratosphere.
Step 2: Recall that the ozone layer absorbs most of the harmful ultraviolet (UV) radiation from the sun.
Step 3: Recognize that depletion of the ozone layer allows more UV radiation to reach the Earth's surface, increasing the risk of skin cancer and mutations.

Why other options are wrong:
- Option A: Acid rain. This is incorrect because acid rain primarily affects ecosystems and structures, not directly causing skin cancer or high mutation rates.
- Option C: $\mathrm{CO}$ pollution. This is incorrect because CO pollution primarily affects respiratory health and does not directly cause skin cancer or high mutation rates.
- Option D: $\mathrm{C}{\mathrm{O}_2}$ pollution. This is incorrect because CO2 pollution contributes to global warming and climate change, not directly causing skin cancer or high mutation rates.

Key Concepts:
- Ozone layer
- Ultraviolet (UV) radiation
- Skin cancer
- Mutations

Memory Aids:
- Ozone shields us from UV radiation.

Quick Tips:
- Remember that ozone depletion is linked to increased UV radiation and its harmful effects.

2 Easy

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Remembering +4 | -1

Which of the following is not an air pollutant?

View answer and explanation

Correct option: A

{\mathrm{N}_2}

Option A (

{\mathrm{N}_2}

) is correct because nitrogen gas is a natural component of air and is not considered a pollutant in its normal concentration.

Solution approach

Correct Answer + Core Reason: ${\mathrm{N}_2}$ . Nitrogen gas is a natural and abundant component of the atmosphere and is not considered a pollutant in its normal concentration.

Step-by-Step Solution:

Step 1: Define Air Pollutant: An air pollutant is a substance in the air that can have adverse effects on humans and the ecosystem.

Step 2: Analyze ${\mathrm{N}_2}$ : Nitrogen gas ( ${\mathrm{N}_2}$ ) makes up about 78% of the Earth's atmosphere and is essential for life. It is not toxic and does not directly contribute to pollution.

Step 3: Analyze ${\mathrm{N}_2}\mathrm{O}$ : Nitrous oxide ( ${\mathrm{N}_2}\mathrm{O}$ ) is a greenhouse gas and contributes to air pollution.

Step 4: Analyze $\mathrm{NO}$ : Nitric oxide ( $\mathrm{NO}$ ) is a pollutant that contributes to smog and acid rain.

Step 5: Analyze $\mathrm{CO}$ : Carbon monoxide ( $\mathrm{CO}$ ) is a toxic gas and a major air pollutant.

Step 6: Conclusion: Therefore, ${\mathrm{N}_2}$ is not an air pollutant.

Why other options are wrong:
- Option B: ${\mathrm{N}_2}\mathrm{O}$ : Nitrous oxide is a greenhouse gas and contributes to air pollution.
- Option C: $\mathrm{NO}$ : Nitric oxide is a pollutant that contributes to smog and acid rain.
- Option D: $\mathrm{CO}$ : Carbon monoxide is a toxic gas and a major air pollutant.

Key Concepts:
- Air pollutants
- Greenhouse gases
- Atmospheric composition

Memory Aids:
- Remember that nitrogen gas is a major component of clean air.

Quick Tips:
- Differentiate between different nitrogen oxides and their roles in pollution.

3 Easy

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Understanding +4 | -1

Which of the following conditions shows the non polluted environment?

View answer and explanation

Correct option: A

pH of rain water is 5.6

Option A (pH of rain water is 5.6) is correct because a pH of 5.6 for rainwater indicates a natural, unpolluted environment due to dissolved carbon dioxide.

Solution approach

Correct Answer + Core Reason: pH of rain water is 5.6. Natural rainwater is slightly acidic due to dissolved CO2.

Step-by-Step Solution:
Step 1: Understand the concept of pH and its relation to acidity and alkalinity.
Step 2: Recall that normal rainwater has a pH of around 5.6 due to the presence of dissolved carbon dioxide, which forms carbonic acid.
Step 3: Recognize that a pH of 5.6 indicates a slightly acidic but unpolluted environment.

Why other options are wrong:
- Option B: Amount of carbon dioxide in the atmosphere is 3%. This is incorrect because the normal amount of carbon dioxide in the atmosphere is around 0.04%, not 3%. A high concentration of CO2 would contribute to pollution and greenhouse effect.
- Option C: Biochemical oxygen demand 10 ppm. This is incorrect because a BOD of 10 ppm indicates a polluted environment. High BOD means there's a large amount of organic matter being decomposed, consuming oxygen.
- Option D: Eutrophication. This is incorrect because eutrophication is a process where excessive nutrients enrich a body of water, leading to increased plant growth and eventual oxygen depletion, indicating a polluted environment.

Key Concepts:
- pH scale
- Acid rain
- Biochemical Oxygen Demand (BOD)
- Eutrophication

Memory Aids:
- pH < 7 is acidic, pH = 7 is neutral, pH > 7 is alkaline
- Normal rain pH ~ 5.6

Quick Tips:
- Remember the normal pH range for rainwater and the implications of high BOD and eutrophication.

4 Easy

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Understanding +4 | -1

The incorrect statement among the following is

View answer and explanation

Correct option: A

Classical smog occurs in warm, dry and sunny climate

Option A (Classical smog occurs in warm, dry and sunny climate) is correct because classical smog (London smog) occurs in cool, humid conditions, not warm, dry, and sunny climates. Photochemical smog occurs in warm, dry and sunny climate.

Solution approach

Correct Answer + Core Reason: Classical smog occurs in warm, dry and sunny climate. Classical smog (London smog) occurs in cool, humid conditions, not warm, dry, and sunny climates. Photochemical smog occurs in warm, dry and sunny climate.

Step-by-Step Solution:

Step 1: Define Classical Smog: Classical smog, also known as London smog or industrial smog, is characterized by smoke, fog, and sulfur dioxide and forms in cool, humid conditions.

Step 2: Define Photochemical Smog: Photochemical smog forms in warm, dry, and sunny climates due to the action of sunlight on nitrogen oxides and volatile organic compounds.

Step 3: Analyze the Statements:
- Classical smog occurs in warm, dry and sunny climate: This statement is incorrect.
- Sodium arsenite is used as herbicide: This statement is correct.
- Fuel obtain from plastic waste contains no lead: This statement is correct.
- Tetra chloro ethene was earlier used as solvent for dry cleaning: This statement is correct.

Step 4: Conclusion: Therefore, the incorrect statement is that classical smog occurs in warm, dry and sunny climate.

Why other options are wrong:
- Option B: Sodium arsenite is used as herbicide: This is a correct statement.
- Option C: Fuel obtain from plastic waste contains no lead: This is a correct statement.
- Option D: Tetra chloro ethene was earlier used as solvent for dry cleaning: This is a correct statement.

Key Concepts:
- Classical smog (London smog)
- Photochemical smog
- Air pollution

Memory Aids:
- Remember the conditions for classical smog (cool, humid) and photochemical smog (warm, sunny).

Quick Tips:
- Differentiate between classical and photochemical smog based on their formation conditions.

5 Easy

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Analyzing +4 | -1

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R

Assertion A: Hydrogen is an environment friendly fuel.
Reason R: Atomic number of hydrogen is 1 and it is very light element.
In the light of the above statements, choose the correct answer from the options given below

View answer and explanation

Correct option: C

Both A and R are true but R is NOT the correct explanation of A

Option C (Both A and R are true but R is NOT the correct explanation of A) is correct because hydrogen is an environment-friendly fuel, and it has an atomic number of 1, but the latter doesn't explain the former.

Solution approach

Correct Answer + Core Reason: Both A and R are true but R is NOT the correct explanation of A. Hydrogen being environment friendly is due to its combustion producing only water, not its atomic number.

Step-by-Step Solution:

Step 1: Analyze Assertion A: Hydrogen is an environment-friendly fuel because its combustion produces primarily water. This is TRUE.

Step 2: Analyze Reason R: Hydrogen has an atomic number of 1 and is a very light element. This is TRUE, but it doesn't explain why hydrogen is environment-friendly.

Step 3: Determine the relationship: Both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion.

Why other options are wrong:
- Option A (Both A and R are true and R is the correct explanation of A): Incorrect because R does not explain A.
- Option B (A is true but R is false): Incorrect because R is true.
- Option D (A is false but R is true): Incorrect because A is true.

Key Concepts:
- Hydrogen as a fuel
- Environmental impact of fuels
- Atomic number

Memory Aids:
- Hydrogen combustion produces water (H2O).

Quick Tips:
- Consider the products of combustion when evaluating the environmental impact of a fuel.
- Distinguish between true statements and statements that provide a causal explanation.

6 Easy

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Remembering +4 | -1

Which of the following is a living component of atmosphere?

View answer and explanation

Correct option: B

Biosphere

Option B (Biosphere) is correct because the biosphere encompasses all living organisms on Earth and their interactions.

Solution approach

Correct Answer + Core Reason: Biosphere. The biosphere includes all living organisms.

Step-by-Step Solution:

Step 1: Define each component of the Earth's system.

Step 2: Lithosphere: The rigid outer part of the Earth, consisting of the crust and upper mantle.

Step 3: Biosphere: The regions of the surface, atmosphere, and hydrosphere of the earth (or analogous parts of other planets) occupied by living organisms.

Step 4: Hydrosphere: All the waters on the earth's surface, such as lakes and seas, and sometimes including water over the earth's surface, such as clouds.

Step 5: Troposphere: The lowest region of the atmosphere, extending from the earth's surface to a height of about 7-20 km.

Step 6: Identify the component that includes living organisms.

Why other options are wrong:
- Option A: Lithosphere is the solid part of the Earth.
- Option C: Hydrosphere is the water part of the Earth.
- Option D: Troposphere is the lowest layer of the atmosphere.

Key Concepts:
- Earth's spheres: lithosphere, biosphere, hydrosphere, atmosphere

Memory Aids:
- Bio- refers to life.

Quick Tips:
- Remember the definitions of the different spheres of the Earth.

7 Easy

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Understanding +4 | -1

Carbon monoxide, emitted by automobiles, prevents transport of oxygen in body due to

View answer and explanation

Correct option: D

Forming stable compound with haemoglobin

Option D (Forming stable compound with haemoglobin) is correct because carbon monoxide binds strongly to haemoglobin, preventing oxygen transport.

Solution approach

Correct Answer + Core Reason: Forming stable compound with haemoglobin. CO has a much higher affinity for hemoglobin than oxygen.

Step-by-Step Solution:
Step 1: Understand the role of hemoglobin in oxygen transport.
Step 2: Recall that carbon monoxide (CO) has a significantly higher affinity for hemoglobin than oxygen (O2).
Step 3: Recognize that CO binds to hemoglobin, forming carboxyhemoglobin, which prevents oxygen from binding and being transported throughout the body.

Why other options are wrong:
- Option A: Combining with oxygen to form carbon dioxide. This is incorrect because CO does not combine with oxygen in the body to form CO2. It binds to hemoglobin.
- Option B: Destruction of haemoglobin. This is incorrect because CO does not destroy hemoglobin; it binds to it, preventing its function.
- Option C: Preventing reaction between oxygen and haemoglobin. This is partially correct, but CO actively binds to hemoglobin, outcompeting oxygen, rather than just preventing the reaction.

Key Concepts:
- Hemoglobin
- Carbon monoxide poisoning
- Affinity of gases for hemoglobin

Memory Aids:
- CO binds more strongly to hemoglobin than O2.

Quick Tips:
- Remember that CO is a silent killer because it is odorless and colorless, and its effects are due to its high affinity for hemoglobin.

8 Easy

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Understanding +4 | -1

Which of the following statements is false?

View answer and explanation

Correct option: D

Oil slick in a sea water increases DO value

Option D (Oil slick in a sea water increases DO value) is correct because oil slicks decrease, not increase, the dissolved oxygen (DO) value in seawater.

Solution approach

Correct Answer + Core Reason: Oil slick in a sea water increases DO value. Oil slicks prevent oxygen from dissolving in water, thus decreasing DO.

Step-by-Step Solution:
Step 1: Understand the concept of Dissolved Oxygen (DO) and its importance for aquatic life.
Step 2: Recall that oil slicks form a barrier on the surface of the water, preventing oxygen from dissolving into the water.
Step 3: Recognize that this leads to a decrease in DO levels, harming aquatic organisms.

Why other options are wrong:
- Option A: The main reason for river water pollution is industrial and domestic sewage discharge. This is correct because industrial and domestic sewage are major sources of water pollution.
- Option B: Surface water contains a lot of organic matter, mineral nutrients and radioactive materials. This is correct because surface water is often exposed to these substances from various sources.
- Option C: Oil spill in sea water causes heavy damage to fishery. This is correct because oil spills can smother marine life, contaminate food sources, and disrupt ecosystems.

Key Concepts:
- Dissolved Oxygen (DO)
- Oil pollution
- Water pollution sources

Memory Aids:
- Oil and water don't mix, and oil prevents oxygen from dissolving in water.

Quick Tips:
- Remember that oil spills are detrimental to aquatic life due to the reduction in dissolved oxygen.

9 Easy

9 of 14

Analyzing +4 | -1

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R.
Assertion A: Polluted water may have a value of BOD of the order of 17 ppm.
Reason R: BOD is a measure of oxygen required to oxidise both the bio-degradable and non-biodegradable organic material in water.
In the light of the above statements, choose the most appropriate answer from the options given below.

View answer and explanation

Correct option: C

A is correct but R is not correct

Option C (A is correct but R is not correct) is correct because while polluted water can have a BOD of 17 ppm, the reason provided is not entirely accurate as BOD measures biodegradable organic material only.

Solution approach

Correct Answer + Core Reason: A is correct but R is not correct. BOD measures oxygen required to oxidize biodegradable organic material, not both biodegradable and non-biodegradable.

Step-by-Step Solution:

Step 1: Analyze Assertion A: Polluted water can indeed have a BOD of around 17 ppm. This is TRUE.

Step 2: Analyze Reason R: BOD is a measure of the oxygen required to oxidize biodegradable organic material in water. It does NOT include non-biodegradable material. This is FALSE.

Step 3: Determine the relationship: Assertion is true, but the Reason is false.

Why other options are wrong:
- Option A (Both A and R are correct and R is the correct explanation of A): Incorrect because R is not correct.
- Option B (Both A and R are correct but R is NOT the correct explanation of A): Incorrect because R is not correct.
- Option D (A is not correct but R is correct): Incorrect because A is correct.

Key Concepts:
- Biochemical Oxygen Demand (BOD)
- Water pollution
- Biodegradable vs. non-biodegradable substances

Memory Aids:
- BOD measures the oxygen demand for BIODEGRADABLE substances.

Quick Tips:
- Understand the definition and limitations of BOD.
- Differentiate between biodegradable and non-biodegradable pollutants.

10 Easy

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Analyzing +4 | -1

Assertion : The archeological studies are based on the radioactive decay of carbon-14 isotope.

Reason : The ration of

C-14

to

C-12

in the animals and plants is same as that in the atmosphere.

View answer and explanation

Correct option: C

If assertion is true but reason is false.

Option C (If assertion is true but reason is false) is correct because archeological studies do rely on C-14 dating, but the ratio of C-14 to C-12 is not the same in living organisms and the atmosphere due to metabolic processes.

Solution approach

Correct Answer + Core Reason: If assertion is true but reason is false. The ratio of C-14 to C-12 is maintained in living organisms but changes after death.

Step-by-Step Solution:

Step 1: Analyze Assertion: Archeological studies are based on the radioactive decay of carbon-14. This is TRUE.

Step 2: Analyze Reason: The ratio of C-14 to C-12 in animals and plants is the same as that in the atmosphere while they are alive. After death, the C-14 decays, changing the ratio. The statement is partially true while the organism is alive, but the reason makes it sound like it remains the same even after death, which is false. Therefore, the reason is FALSE.

Step 3: Determine the relationship: Assertion is true, but the Reason is false.

Why other options are wrong:
- Option A (If both assertion and reason are true and the reason is the correct explanation of the assertion): Incorrect because the reason is false.
- Option B (If both assertion and reason are true but reason is not the correct explanation of the assertion): Incorrect because the reason is false.
- Option D (If the assertion and reason both are false): Incorrect because the assertion is true.

Key Concepts:
- Radiocarbon dating
- Radioactive decay
- Isotopes of carbon (C-14, C-12)

Memory Aids:
- C-14 dating relies on the decay of C-14 after an organism dies.

Quick Tips:
- Remember that C-14 dating is effective for organic materials.
- Understand the process of radioactive decay and its application in dating.

11 Easy

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Remembering +4 | -1

Cyclone collector is used for minimising

View answer and explanation

Correct option: B

Air pollution

Option B (Air pollution) is correct because cyclone collectors are designed to remove particulate matter from air streams, thus minimizing air pollution.

Solution approach

Correct Answer + Core Reason: Air pollution. Cyclone collectors are used to remove particulate matter from air.

Step-by-Step Solution:

Step 1: Define the function of a cyclone collector.

Step 2: A cyclone collector is a type of air pollution control equipment that uses inertia to remove particulate matter from a gas stream.

Step 3: The gas stream is forced to flow in a spiral path inside a cylindrical or conical chamber, and centrifugal force causes the particles to move towards the walls of the chamber, where they are collected.

Step 4: Determine the type of pollution minimized by cyclone collectors.

Why other options are wrong:
- Option A: Radioactive pollution is minimized by specific containment and disposal methods, not cyclone collectors.
- Option C: Noise pollution is minimized by soundproofing and other

12 Easy

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Remembering +4 | -1

Mesosphere and thermosphere are collectively known as

View answer and explanation

Correct option: C

Ionosphere

Option C (Ionosphere) is correct because the ionosphere is the region of Earth's upper atmosphere, including the mesosphere and thermosphere, where ionization occurs.

Solution approach

Correct Answer + Core Reason: Ionosphere. The ionosphere is a region of the Earth's upper atmosphere that includes the mesosphere and thermosphere and is characterized by ionization.

Step-by-Step Solution:

Step 1: Define Mesosphere: The mesosphere is the third layer of the atmosphere, located above the stratosphere and below the thermosphere.

Step 2: Define Thermosphere: The thermosphere is the layer of the atmosphere directly above the mesosphere and below the exosphere.

Step 3: Define Ionosphere: The ionosphere is a region of the upper atmosphere, from about 60 km to 1000 km altitude, characterized by the presence of ions and free electrons. It includes parts of the mesosphere, thermosphere, and exosphere.

Step 4: Conclusion: Therefore, mesosphere and thermosphere are collectively known as the ionosphere.

Why other options are wrong:
- Option A: Exosphere: The exosphere is the outermost layer of the atmosphere, beyond the thermosphere.
- Option B: Thermopause: The thermopause is the boundary between the thermosphere and the exosphere.
- Option D: Interstellar region: The interstellar region is the space between star systems.

Key Concepts:
- Atmospheric layers (mesosphere, thermosphere, exosphere, ionosphere)
- Ionization

Memory Aids:
- Think of "ions" in "ionosphere" to remember that it's a region with ionized particles.

Quick Tips:
- The ionosphere is important for radio wave propagation.

13 Easy

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Remembering +4 | -1

What does

\mathrm{BO}{\mathrm{D}_5}

represent?

View answer and explanation

Correct option: C

Dissolved oxygen consumed in five days

Option C (Dissolved oxygen consumed in five days) is correct because BOD5 specifically measures the amount of oxygen consumed by microorganisms in a water sample over a 5-day period.

Solution approach

Correct Answer + Core Reason: Dissolved oxygen consumed in five days. $\mathrm{BO}{\mathrm{D}_5}$ represents the amount of dissolved oxygen consumed by microorganisms in a water sample over a 5-day period at a specific temperature.

Step-by-Step Solution:

Step 1: Define BOD5: Biochemical Oxygen Demand (BOD) is the amount of dissolved oxygen needed by aerobic biological organisms to break down organic material present in a given water sample at certain temperature over a specific time period.

Step 2: Understand the '5': The subscript 5 in $\mathrm{BO}{\mathrm{D}_5}$ indicates that the measurement is taken over a period of 5 days.

Step 3: Relate BOD5 to water quality: A higher BOD5 indicates a larger amount of organic pollution in the water, which requires more oxygen to be consumed by microorganisms.

Step 4: Conclusion: Therefore, $\mathrm{BO}{\mathrm{D}_5}$ represents the dissolved oxygen consumed in five days.

Why other options are wrong:
- Option A: Biological ozone depletion in five days: This is incorrect because BOD is related to oxygen consumption by microorganisms, not ozone depletion.
- Option B: Dissolved oxygen left after five days: This is incorrect because BOD measures the oxygen consumed, not the oxygen remaining.
- Option D: Micro-organisms killed by ozone in sewage treatment plants in five hours: This is incorrect because BOD is about oxygen consumption, not the effect of ozone on microorganisms.

Key Concepts:
- Biochemical Oxygen Demand (BOD)
- Water quality assessment
- Microbial activity

Memory Aids:
- BOD: Biological Oxygen Demand, think of it as the demand for oxygen by living organisms.

Quick Tips:
- BOD is a key indicator of water pollution levels. Higher BOD means more pollution.

14 Easy

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Remembering +4 | -1

Green house effect is caused by

View answer and explanation

Correct option: D

\mathrm{C}{\mathrm{O}_2}

Option D (

\mathrm{C}{\mathrm{O}_2}

) is correct because carbon dioxide is a major greenhouse gas that traps heat in the atmosphere.

Solution approach

Correct Answer + Core Reason: $\mathrm{C}{\mathrm{O}_2}$ . Carbon dioxide is a major greenhouse gas.

Step-by-Step Solution:

Step 1: Identify the greenhouse gases.

Step 2: Greenhouse gases are those that absorb and emit radiant energy within the thermal infrared range.

Step 3: Common greenhouse gases include water vapor ( $\mathrm{H}_2\mathrm{O}$ ), carbon dioxide ( $\mathrm{C}{\mathrm{O}_2}$ ), methane ( $\mathrm{CH}_4$ ), nitrous oxide ( $\mathrm{N}_2\mathrm{O}$ ), and ozone ( $\mathrm{O}_3$ ).

Step 4: Among the given options, only carbon dioxide is a well-known greenhouse gas.

Why other options are wrong:
- Option A: $\mathrm{N}{\mathrm{O}_2}$ is a pollutant but not a major greenhouse gas compared to $\mathrm{CO}_2$ .
- Option B: $\mathrm{CO}$ is a pollutant but not a major greenhouse gas compared to $\mathrm{CO}_2$ .
- Option C: $\mathrm{NO}$ is a pollutant but not a major greenhouse gas compared to $\mathrm{CO}_2$ .

Key Concepts:
- Greenhouse effect
- Greenhouse gases

Memory Aids:
- Remember the major greenhouse gases: $\mathrm{CO}_2$ , $\mathrm{CH}_4$ , $\mathrm{N}_2\mathrm{O}$ , $\mathrm{H}_2\mathrm{O}$ .

Quick Tips:
- Know the major contributors to the greenhouse effect.

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Environmental chemistry practice · Easy

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