ENVIRONMENTAL CHEMISTRY MCQs for JEE CHEMISTRY — Medium

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Given below are two Statements:
Statement I: Classical smog occurs in cool humid climate. It is a reducing mixture of smoke, fog and sulphur dioxide.
Statement II: Photochemical smog has components, ozone, nitric oxide, acrolein, formaldehyde, PAN etc.
In the light of the above statements, choose the most appropriate answer from the options given below.

View answer and explanation

Correct option: A

Both Statement I and Statement II are correct.

Option A is correct because both statements accurately describe classical and photochemical smog, respectively.

Solution approach

Correct Answer + Core Reason: Both Statement I and Statement II are correct. Both statements are factually correct regarding the characteristics of classical and photochemical smog.

Step-by-Step Solution:

Step 1: Analyze Statement I: Classical smog is indeed characterized by cool, humid climates and is a reducing mixture containing smoke, fog, and sulfur dioxide.

Step 2: Analyze Statement II: Photochemical smog does contain components like ozone, nitric oxide, acrolein, formaldehyde, and PAN (peroxyacyl nitrates).

Step 3: Combine the analyses: Both statements are accurate descriptions of their respective types of smog.

Why other options are wrong:
- Option B: Incorrect because both statements are correct.
- Option C: Incorrect because both statements are correct.
- Option D: Incorrect because Statement I is also correct.

Key Concepts:
- Classical Smog
- Photochemical Smog
- Air Pollution

Memory Aids:
- Classical smog: Cool, humid, reducing (smoke, fog, SO2)
- Photochemical smog: Ozone, NOx, PAN, etc.

Quick Tips:
- Remember the key components and conditions associated with each type of smog.

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UV radiations bring about

View answer and explanation

Correct option: A

Skin cancer

Option A (Skin cancer) is correct because UV radiation damages DNA in skin cells, leading to an increased risk of skin cancer.

Solution approach

Correct Answer + Core Reason: Skin cancer because UV radiation damages DNA in skin cells.

Step-by-Step Solution:
Step 1: Recall the effects of UV radiation on living organisms.
Step 2: Understand that UV radiation can damage DNA, leading to mutations.
Step 3: Recognize that skin cells are particularly vulnerable to UV radiation due to direct exposure.
Step 4: Understand that DNA damage in skin cells can lead to uncontrolled cell growth and skin cancer.

Why other options are wrong:
- Option B: Mouth cancer is more commonly associated with tobacco and alcohol use.
- Option C: Lung cancer is more commonly associated with smoking and air pollution.
- Option D: Liver cancer is more commonly associated with hepatitis and alcohol abuse.

Key Concepts:
- UV radiation
- DNA damage
- Skin cancer

Memory Aids:
- UV = Skin

Quick Tips:
- Protect yourself from UV radiation by using sunscreen and wearing protective clothing.

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Which of the following is a primary pollutant?

View answer and explanation

Correct option: A

CO

Option A (

CO

) is correct because Carbon Monoxide (

CO

) is a primary pollutant, directly emitted from sources.

Solution approach

Correct Answer + Core Reason: $CO$ . Carbon monoxide is a primary pollutant.

Step-by-Step Solution:
Step 1: Define primary and secondary pollutants.
Step 2: Primary pollutants are directly emitted from a source.
Step 3: Carbon monoxide ( $CO$ ) is a primary pollutant.

Why other options are wrong:
- Option B: $PAN$ (Peroxyacyl nitrates) is a secondary pollutant formed from reactions in the atmosphere.
- Option C: Aldehydes can be both primary and secondary pollutants, but in this context, they are more often secondary.
- Option D: ${\mathrm{H}_2}\mathrm{S}{\mathrm{O}_4}$ (Sulfuric acid) is a secondary pollutant formed from reactions in the atmosphere.

Key Concepts:
- Environmental pollution
- Primary pollutants
- Secondary pollutants

Memory Aids:
- Primary = Directly emitted; Secondary = Formed in the atmosphere.

Quick Tips:
- Knowing the difference between primary and secondary pollutants is essential.

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Persons working in cement plants and limestone quarries are more prone to disease like:

View answer and explanation

Correct option: C

Silicosis

Option C (Silicosis) is correct because silicosis is a lung disease caused by inhaling silica dust, which is common in cement plants and limestone quarries.

Solution approach

Correct Answer + Core Reason: Silicosis. Silicosis is caused by inhaling silica dust, common in cement plants and limestone quarries.

Step-by-Step Solution:

Step 1: Identify the occupational hazards associated with cement plants and limestone quarries.

Step 2: Recognize that these environments contain high levels of silica dust.

Step 3: Recall that silicosis is a lung disease caused by the inhalation of silica dust.

Step 4: Connect the occupational hazard to the specific disease.

Why other options are wrong:
- Option A: Cancer: While exposure to certain substances in these environments might increase cancer risk over long periods, it's not the most direct and common disease.
- Option B: Asthma: Asthma can be aggravated by dust, but silicosis is more directly linked to silica exposure.
- Option D: Pneumoconiosis: This is a general term for lung diseases caused by dust inhalation, but silicosis is the specific type most associated with silica dust.

Key Concepts:
- Occupational health hazards
- Silicosis
- Silica dust

Memory Aids:
- \"Silica = Silicosis.\"

Quick Tips:
- Focus on the specific dust involved (silica) to identify the correct disease.

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According to recent reports, acid rain is caused by

View answer and explanation

Correct option: B

Excessive release of

\mathrm{NO}_2

and

\mathrm{SO}_2

in atmosphere by burning of fossil fuel.

Option B (Excessive release of

\mathrm{NO}_2

and

\mathrm{SO}_2

in atmosphere by burning of fossil fuel) is correct because acid rain is primarily caused by nitrogen and sulfur oxides released from burning fossil fuels.

Solution approach

Correct Answer + Core Reason: Excessive release of $\mathrm{NO}_2$ and $\mathrm{SO}_2$ in atmosphere by burning of fossil fuel. These gases react with water to form acids.

Step-by-Step Solution:

Step 1: Identify the primary pollutants responsible for acid rain.\nThe primary pollutants responsible for acid rain are nitrogen dioxide ( $\mathrm{NO}_2$ ) and sulfur dioxide ( $\mathrm{SO}_2$ ).

Step 2: Understand the formation of acid rain.\nThese gases are released into the atmosphere primarily from the burning of fossil fuels in industries and vehicles.\nIn the atmosphere, these gases react with water, oxygen, and other chemicals to form sulfuric acid ( $\mathrm{H}_2\mathrm{SO}_4$ ) and nitric acid ( $\mathrm{HNO}_3$ ).\nThese acids then fall to the earth as acid rain.

Step 3: Final Answer\nAcid rain is caused by the excessive release of $\mathrm{NO}_2$ and $\mathrm{SO}_2$ in the atmosphere by the burning of fossil fuels.

Why other options are wrong:
- Option A: Excessive release of $\mathrm{CO}_2$ is incorrect because while $\mathrm{CO}_2$ contributes to climate change, it is not the primary cause of acid rain.
- Option C: Excessive release of $\mathrm{NH}_3$ is incorrect because ammonia can contribute to air pollution but is not the primary cause of acid rain. It can neutralize acids to some extent.
- Option D: Excessive release of $\mathrm{CO}$ is incorrect because carbon monoxide is a toxic gas but does not directly cause acid rain.

Key Concepts:
- Acid rain formation
- Primary pollutants: $\mathrm{NO}_2$ and $\mathrm{SO}_2$
- Sources of pollutants: Burning of fossil fuels

Memory Aids:
- Remember that acid rain involves "oxides of nitrogen and sulfur".

Quick Tips:
- Focus on the gases that directly form acids when dissolved in water.

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The BOD value of clean water is

View answer and explanation

Correct option: A

< 5

ppm

Option A (

< 5

ppm) is correct because clean water has a low BOD value, indicating minimal organic pollution.

Solution approach

Correct Answer + Core Reason: $< 5$ ppm. Clean water has a low BOD because it contains little organic matter.

Step-by-Step Solution:

Step 1: Define BOD (Biochemical Oxygen Demand).

Step 2: BOD is the amount of dissolved oxygen needed by aerobic biological organisms to break down organic material present in a water sample at certain temperature over a specific time period.

Step 3: Clean water has low organic content, hence low BOD.

Step 4: BOD value for clean water is less than 5 ppm.

Why other options are wrong:
- Option B: $< 15 \mathrm{ppm}$ : This value indicates moderately polluted water.
- Option C: $>15 \mathrm{ppm}$ : This value indicates highly polluted water.
- Option D: $>17 \mathrm{ppm}$ : This value indicates severely polluted water.

Key Concepts:
- Biochemical Oxygen Demand (BOD)
- Water pollution

Memory Aids:
- Low BOD = Good water quality

Quick Tips:
- Remember the BOD ranges for different levels of water pollution.

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Photochemical smog consists of excessive amount of X, in
addition to aldehydes, ketones, peroxyacetyl nitrate (PAN), and so forth, X is :

View answer and explanation

Correct option: C

{O_3}

Option C (

{O_3}

) is correct because photochemical smog contains ozone (

O_3

) along with other pollutants like aldehydes, ketones, and PAN.

Solution approach

Correct Answer + Core Reason: ${O_3}$ . Ozone is a key component of photochemical smog.

Step-by-Step Solution:

Step 1: Define Photochemical Smog: Photochemical smog is a type of air pollution that forms when sunlight reacts with nitrogen oxides and volatile organic compounds (VOCs) in the atmosphere.

Step 2: Identify the components of photochemical smog: The main components of photochemical smog include nitrogen oxides ( $NO_x$ ), volatile organic compounds (VOCs), ozone ( $O_3$ ), peroxyacetyl nitrate (PAN), aldehydes, and ketones.

Step 3: Explain the formation of ozone: Ozone is formed in photochemical smog through a series of reactions involving nitrogen oxides and VOCs in the presence of sunlight.

Why other options are wrong:
- Option A: CO (carbon monoxide) is a common air pollutant but not a primary component of photochemical smog.
- Option B: $CH_4$ (methane) is a greenhouse gas and a VOC, but ozone is a more significant component of photochemical smog.
- Option D: $CO_2$ (carbon dioxide) is a greenhouse gas but not a primary component of photochemical smog.

Key Concepts:
- Photochemical smog
- Air pollution
- Ozone formation
- Nitrogen oxides
- Volatile organic compounds (VOCs)

Memory Aids:
- Remember that ozone is a key component of photochemical smog.

Quick Tips:
- Know the major pollutants involved in air pollution.

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Salvarsan is an antimicrobial agent which is used to cure:-

View answer and explanation

Correct option: B

Syphilis

Option B (Syphilis) is correct because Salvarsan, also known as arsphenamine, was historically used to treat syphilis.

Solution approach

Correct Answer + Core Reason: Syphilis. Salvarsan is used to treat syphilis.

Step-by-Step Solution:

Step 1: Recall the uses of Salvarsan.

Step 2: Salvarsan is an antimicrobial agent.

Step 3: It was historically used to treat syphilis.

Why other options are wrong:
- Option A: Allergy is not treated with Salvarsan.
- Option C: Depression is not treated with Salvarsan.
- Option D: Malaria is not treated with Salvarsan.

Key Concepts:
- Salvarsan
- Antimicrobial agents
- Syphilis

Memory Aids:
- Salvarsan = Syphilis

Quick Tips:
- Remember the uses of common drugs.

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Which of the following gases present in air protects life on the earth from the harmful effects of

UV

rays from the sun?

View answer and explanation

Correct option: D

Ozone

Option D (Ozone) is correct because the ozone layer in the atmosphere absorbs harmful UV rays from the sun, protecting life on Earth.

Solution approach

Correct Answer + Core Reason: Ozone. Ozone ( $O_3$ ) absorbs harmful ultraviolet (UV) radiation from the sun.

Step-by-Step Solution:

Step 1: Recall the composition of the atmosphere.

Step 2: Identify the gases present in the atmosphere: Carbon dioxide, Nitrogen, Oxygen, and Ozone.

Step 3: Recognize that the ozone layer is responsible for absorbing UV radiation.

Step 4: Ozone ( $O_3$ ) absorbs UV radiation, protecting life on Earth.

Why other options are wrong:
- Option A: Carbon dioxide is a greenhouse gas but does not primarily absorb UV radiation.
- Option B: Nitrogen is a major component of the atmosphere but does not absorb UV radiation.
- Option C: Oxygen is essential for respiration but does not primarily absorb UV radiation like ozone does.

Key Concepts:
- Atmospheric composition
- Ozone layer
- UV radiation
- Environmental protection

Memory Aids:
- Remember that ozone protects us from the sun's harmful UV rays.

Quick Tips:
- Understand the role of different gases in the atmosphere.

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The ozone layer forms naturally by

View answer and explanation

Correct option: B

The interaction of UV radiation with oxygen.

Option B (The interaction of UV radiation with oxygen) is correct because UV radiation breaks down oxygen molecules into single oxygen atoms, which then combine with other oxygen molecules to form ozone.

Solution approach

Correct Answer + Core Reason: The interaction of UV radiation with oxygen is how the ozone layer forms naturally.

Step-by-Step Solution:

Step 1: Understand the process of ozone formation. Ozone ( $O_3$ ) is formed when oxygen molecules ( $O_2$ ) absorb UV radiation from the sun.

Step 2: Write the chemical reactions. The UV radiation breaks the $O_2$ molecule into two oxygen atoms ( $O$ ). These oxygen atoms then react with other $O_2$ molecules to form ozone:
$O_2 + h\nu \rightarrow O + O$
$O + O_2 \rightarrow O_3$

Why other options are wrong:
- Option A: CFCs (chlorofluorocarbons) actually destroy the ozone layer, not form it. They catalyze the breakdown of ozone.
- Option C: IR (infrared) radiation does not have enough energy to break down oxygen molecules to form ozone. IR radiation is primarily associated with heat.
- Option D: While water vapor can be involved in atmospheric chemistry, it is not the primary mechanism for ozone formation.

Key Concepts:
- Ozone formation
- UV radiation
- Chemical reactions in the atmosphere

Memory Aids:
- UV breaks $O_2$ to make $O_3$

Quick Tips:
- Remember that UV radiation is essential for ozone formation, while CFCs are detrimental.

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The formation of

{O}_3

in upper part of atmosphere is catalyzed by

View answer and explanation

Correct option: B

NO

Option B (

NO

) is correct because nitrogen oxide acts as a catalyst in the formation of ozone in the upper atmosphere.

Solution approach

Correct Answer + Core Reason: $NO$ . Nitrogen oxide catalyzes the formation of ozone.

Step-by-Step Solution:

Step 1: Identify the process: Ozone formation in the upper atmosphere.

Step 2: Recall the role of catalysts: Catalysts speed up reactions without being consumed.

Step 3: Recognize the catalyst: Nitrogen oxides (specifically NO) are known to catalyze ozone formation and destruction.

Step 4: Conclusion: NO acts as a catalyst in the formation of O3.

Why other options are wrong:
- Option A: ${N}_2$ is a major component of the atmosphere but does not catalyze ozone formation.
- Option C: ${CO}$ is a pollutant and does not catalyze ozone formation.
- Option D: ${CO}_2$ is a greenhouse gas and does not catalyze ozone formation.

Key Concepts:
- Catalysis
- Ozone formation
- Atmospheric chemistry

Memory Aids:
- Remember that NO is involved in both ozone formation and depletion cycles.

Quick Tips:
- Recall common catalysts in atmospheric reactions.

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The compound which reacts with ozone very rapidly to liberate oxygen is

View answer and explanation

Correct option: A

{NO}

Option A (

{NO}

) is correct because nitric oxide reacts rapidly with ozone to produce nitrogen dioxide and oxygen.

Solution approach

Correct Answer + Core Reason: ${NO}$ . Nitric oxide reacts quickly with ozone to form nitrogen dioxide and oxygen.

Step-by-Step Solution:

Step 1: Recall the reactions of ozone with various compounds.

Step 2: Recognize that nitric oxide (NO) reacts rapidly with ozone ( $O_3$ ).

Step 3: Write the chemical equation: $NO + O_3 \rightarrow NO_2 + O_2$ .

Step 4: Understand that this reaction is fast due to the instability of NO and its ability to readily react with ozone.

Why other options are wrong:
- Option B: $CO_2$ is relatively inert and does not react rapidly with ozone.
- Option C: $NO_2$ is a product of the reaction between NO and ozone, not a reactant that liberates oxygen rapidly.
- Option D: $SO_3$ reacts with ozone much slower than NO.

Key Concepts:
- Ozone chemistry
- Reactions of oxides

Memory Aids:
- NO loves ozone!

Quick Tips:
- Remember the common reactions of ozone with different oxides.

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Maximum limit of nitrate in drinking water is ____ ppm and its excess concentration causes ____

View answer and explanation

Correct option: B

50 ppm, blue baby syndrome

Option B (50 ppm, blue baby syndrome) is correct because the maximum limit of nitrate in drinking water is 50 ppm, and exceeding this limit can cause methemoglobinemia, also known as blue baby syndrome.

Solution approach

Correct Answer + Core Reason: 50 ppm, blue baby syndrome. Excess nitrate in drinking water leads to blue baby syndrome.

Step-by-Step Solution:

Step 1: Recall the permissible limit of nitrate in drinking water.

Step 2: The maximum limit of nitrate ( $NO_3^-$ ) in drinking water is 50 ppm.

Step 3: Excess nitrate in drinking water can cause methemoglobinemia, also known as blue baby syndrome, especially in infants.

Why other options are wrong:
- Option A: Kidney damage is not the primary effect of excess nitrate.
- Option C: 10 ppm is too low for the nitrate limit, and tooth decay is related to fluoride, not nitrate.
- Option D: Laxative effect is not directly associated with nitrate.

Key Concepts:
- Water pollution
- Nitrate contamination
- Health effects of nitrates

Memory Aids:
- Nitrate - Blue Baby

Quick Tips:
- Remember the permissible limits of common pollutants in drinking water and their associated health effects.

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Cause of Stratosphere's ozone layer depletion

View answer and explanation

Correct option: A

\mathrm{CF}_2 \mathrm{Cl}_2

Option A (

\mathrm{CF}_2 \mathrm{Cl}_2

) is correct because chlorofluorocarbons (CFCs) like dichlorodifluoromethane are major contributors to ozone depletion.

Solution approach

Correct Answer + Core Reason: $\mathrm{CF}_2 \mathrm{Cl}_2$ . CFCs are the primary cause of ozone depletion.

Step-by-Step Solution:

Step 1: Identify the main cause of ozone layer depletion.

Step 2: Chlorofluorocarbons (CFCs) are the main cause of ozone depletion in the stratosphere.

Step 3: $\mathrm{CF}_2 \mathrm{Cl}_2$ (dichlorodifluoromethane) is a common CFC that releases chlorine atoms upon exposure to UV radiation, which then catalyze the destruction of ozone molecules.

Step 4: The other options are fluorocarbons or chlorocarbons, but CFCs are the most significant contributors.

Why other options are wrong:
- Option B: $\mathrm{C}_6 \mathrm{~F}_{16}$ is incorrect because it is a fluorocarbon, but not a primary cause of ozone depletion.
- Option C: $\mathrm{C}_6 \mathrm{H}_6 \mathrm{~F}_6$ is incorrect because it is a fluorocarbon, but not a primary cause of ozone depletion.
- Option D: $\mathrm{C}_6 \mathrm{Cl}_6$ is incorrect because it is a chlorocarbon, but CFCs are the main cause of ozone depletion.

Key Concepts:
- Ozone Layer Depletion
- Chlorofluorocarbons (CFCs)

Memory Aids:
- CFCs = Ozone depletion

Quick Tips:
- Remember the role of CFCs in ozone depletion.

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Which of the following region is the coldest?

View answer and explanation

Correct option: C

Mesosphere

Option C (Mesosphere) is correct because the mesosphere is the coldest layer of the atmosphere, with temperatures reaching as low as -100°C.

Solution approach

Correct Answer + Core Reason: Mesosphere is the coldest region of the atmosphere.

Step-by-Step Solution:

Step 1: Recall the layers of the atmosphere: Troposphere, Stratosphere, Mesosphere, Thermosphere.

Step 2: Consider the temperature profiles of each layer:
- Troposphere: Temperature decreases with altitude.
- Stratosphere: Temperature increases with altitude due to ozone absorption.
- Mesosphere: Temperature decreases with altitude, reaching the coldest temperatures.
- Thermosphere: Temperature increases with altitude due to absorption of high-energy radiation.

Step 3: Identify the mesosphere as the coldest region.

Why other options are wrong:
- Option A: The stratosphere is warmer than the troposphere and mesosphere due to ozone absorption.
- Option B: The troposphere is the warmest layer, closest to the Earth's surface.
- Option D: The thermosphere is very hot due to absorption of high-energy radiation.

Key Concepts:
- Atmospheric layers
- Temperature profiles of the atmosphere

Memory Aids:
- Mesosphere = Coldest

Quick Tips:
- Remember the order of the atmospheric layers and their temperature trends.

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Which one of the following gases is reported to retard photosynthesis?

View answer and explanation

Correct option: D

N{O_2}

Option D (

N{O_2}

) is correct because nitrogen dioxide damages plant leaves, thus retarding photosynthesis.

Solution approach

Correct Answer + Core Reason: $N{O_2}$ . Nitrogen dioxide damages plant leaves and retards photosynthesis.

Step-by-Step Solution:

Step 1: Identify the question type: This is a conceptual question about the effects of gases on photosynthesis.

Step 2: Recall the process of photosynthesis: Plants use carbon dioxide, water, and sunlight to produce glucose and oxygen.

Step 3: Consider the effects of each gas:
- CO can interfere with plant respiration.
- CFCs deplete the ozone layer, indirectly affecting photosynthesis.
- $CO_2$ is a reactant in photosynthesis, but excessive amounts can have negative effects in the long term.
- $N{O_2}$ is a pollutant that can directly damage plant tissues.

Step 4: Determine the gas that directly retards photosynthesis: $N{O_2}$ is known to damage leaves, thus directly hindering photosynthesis.

Why other options are wrong:
- **Option A ( $CO$ ): Carbon monoxide primarily affects respiration, not directly photosynthesis.
- Option B ( $CFCs$ ): Chlorofluorocarbons deplete the ozone layer, which indirectly affects photosynthesis by increasing UV radiation, but it is not a direct inhibitor.
- Option C ( $C{O_2}$ ): Carbon dioxide is a reactant in photosynthesis; while excessive amounts can have indirect negative effects, it doesn't directly retard the process.

Key Concepts:
- Photosynthesis
- Air pollution
- Effects of gases on plants

Memory Aids:**
- Remember that $N{O_2}$ is a common air pollutant that damages plant tissues.

Quick Tips:
- Consider the direct effects of each gas on plant physiology.

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The correct set of species responsible for the photochemical smog is

View answer and explanation

Correct option: C

NO,N{O_2},{O_3}

and hydrocarbons

Option C (

NO,N{O_2},{O_3}

and hydrocarbons) is correct because these species are directly involved in the photochemical reactions that produce smog.

Solution approach

Correct Answer + Core Reason: $NO,N{O_2},{O_3}$ and hydrocarbons. These are the key components of photochemical smog.

Step-by-Step Solution:

Step 1: Recall the formation of photochemical smog.

Step 2: Understand that nitrogen oxides (NO and NO2) and ozone (O3) are key components of photochemical smog, along with unburnt hydrocarbons.

Step 3: Recognize that these species are formed through photochemical reactions involving sunlight.

Why other options are wrong:
- Option A: N2 is not directly involved in photochemical smog formation.
- Option B: CO2 and SO2 are pollutants but not the primary drivers of photochemical smog.
- Option D: N2 and O2 are major components of air but not directly involved in photochemical smog formation.

Key Concepts:
- Photochemical smog
- Nitrogen oxides
- Ozone
- Hydrocarbons

Memory Aids:
- Remember the key components of photochemical smog: NOx, O3, and hydrocarbons.

Quick Tips:
- Know the major air pollutants and their sources.

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Which of the following is responsible for peeling of ozone umbrella?

View answer and explanation

Correct option: C

\mathrm{CFC}s

Option C (

\mathrm{CFC}s

) is correct because Chlorofluorocarbons (CFCs) are the primary cause of ozone depletion in the stratosphere.

Solution approach

Correct Answer + Core Reason: $\mathrm{CFC}s$ . CFCs release chlorine atoms in the stratosphere, which catalyze the breakdown of ozone.

Step-by-Step Solution:

Step 1: Identify the location of the ozone layer. The ozone layer is located in the stratosphere.

Step 2: Understand the function of the ozone layer. The ozone layer absorbs harmful UV radiation from the sun.

Step 3: Identify the primary cause of ozone depletion. Chlorofluorocarbons (CFCs) are the main cause of ozone depletion.

Step 4: Explain how CFCs deplete the ozone layer. CFCs release chlorine atoms when exposed to UV radiation in the stratosphere. These chlorine atoms act as catalysts, breaking down ozone molecules (O3) into oxygen molecules (O2).

Why other options are wrong:
- Option A: PAN (Peroxyacyl nitrates) are secondary pollutants found in photochemical smog, but they are not the primary cause of ozone depletion.
- Option B: Coal burning contributes to air pollution and acid rain but is not the primary cause of ozone depletion.
- Option D: $\mathrm{C}{\mathrm{O}_2}$ (Carbon dioxide) is a greenhouse gas that contributes to global warming but is not the primary cause of ozone depletion.

Key Concepts:
- Ozone layer
- Ozone depletion
- Chlorofluorocarbons (CFCs)
- Catalytic breakdown

Memory Aids:
- CFCs = Chlorine destroys Ozone!

Quick Tips:
- Remember that CFCs are the main culprit for ozone depletion.

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Turpentine oil can be purified by this process

View answer and explanation

Correct option: A

Steam distillation

Option A (Steam distillation) is correct because turpentine oil is purified by steam distillation due to its immiscibility with water and high vapor pressure.

Solution approach

Correct Answer + Core Reason: Steam distillation. Turpentine oil is purified by steam distillation.

Step-by-Step Solution:
Step 1: Identify the appropriate purification method for turpentine oil.
Step 2: Turpentine oil is immiscible with water and has a high vapor pressure.
Step 3: Steam distillation is used to purify turpentine oil.

Why other options are wrong:
- Option B: Vacuum distillation is used for high-boiling liquids that decompose at their boiling points.
- Option C: Simple distillation is used for liquids with significantly different boiling points.
- Option D: Fractional distillation is used for liquids with close boiling points.

Key Concepts:
- Steam distillation
- Purification methods

Memory Aids:
- Remember that steam distillation is used for immiscible liquids with high vapor pressure.

Quick Tips:
- Know the appropriate purification methods for different types of liquids.

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Which of the following gas is the major contributor of global warming?

View answer and explanation

Correct option: A

C{O_2}

Option A (

C{O_2}

) is correct because carbon dioxide is the most significant contributor to global warming due to its abundance and long atmospheric lifetime.

Solution approach

Correct Answer + Core Reason: $C{O_2}$ . Carbon dioxide is the major contributor to global warming.

Step-by-Step Solution:
Step 1: Recall the greenhouse gases and their contributions to global warming.
Step 2: Carbon dioxide is a major byproduct of fossil fuel combustion and has a significant impact on global warming.

Why other options are wrong:
- Option B: $C{H_4}$ : Methane is a potent greenhouse gas, but its overall contribution is less than carbon dioxide.
- Option C: Freons: Freons are potent greenhouse gases, but their concentrations are lower than carbon dioxide.
- Option D: ${N_2}O$ : Nitrous oxide is a potent greenhouse gas, but its overall contribution is less than carbon dioxide.

Key Concepts:
- Greenhouse effect
- Global warming
- Greenhouse gases

Memory Aids:
- Carbon dioxide is the most abundant greenhouse gas.

Quick Tips:
- Know the major greenhouse gases and their sources.

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Many people died in London in 1952 as a result of air pollution producing……

View answer and explanation

Correct option: C

Smog

Option C (Smog) is correct because the air pollution in London in 1952 resulted in a dense smog that caused respiratory problems and deaths.

Solution approach

Correct Answer + Core Reason: Smog. The London smog of 1952 caused many deaths due to air pollution.

Step-by-Step Solution:

Step 1: The question asks about the type of air pollution that caused deaths in London in 1952.

Step 2: Recall the different types of air pollution: mist, fog, smog, sleet.

Step 3: Smog is a mixture of smoke and fog, often caused by industrial pollution, which was prevalent in London at the time.

Step 4: The London smog of 1952 was a severe air pollution event.

Step 5: Conclusion: The answer is Smog.

Why other options are wrong:
- Option A: Mist is a light suspension of liquid droplets in the air, reducing visibility, but not as severe as smog.
- Option B: Fog is a dense suspension of water droplets in the air, reducing visibility, but not necessarily containing pollutants like smog.
- Option D: Sleet is a form of precipitation consisting of ice pellets mixed with rain or snow; it's not related to air pollution.

Key Concepts:
- Air pollution
- Smog formation

Memory Aids:
- Smog = Smoke + Fog

Quick Tips:
- Understand the difference between mist, fog, smog, and sleet.

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Choose the process that is not the reason of increase of

\mathrm{CO}_2

concentration in atmosphere.

View answer and explanation

Correct option: C

Photosynthesis

Option C (Photosynthesis) is correct because photosynthesis consumes CO2 from the atmosphere, thus reducing its concentration.

Solution approach

Correct Answer + Core Reason: Photosynthesis. Photosynthesis consumes CO2, reducing its atmospheric concentration.

Step-by-Step Solution:

Step 1: Analyze each process:
- Decay of animals: Releases CO2 into the atmosphere.
- Respiration: Releases CO2 into the atmosphere.
- Photosynthesis: Consumes CO2 from the atmosphere.
- Burning of petrol: Releases CO2 into the atmosphere.

Step 2: Identify the process that decreases CO2 concentration. Photosynthesis uses CO2 to produce glucose and oxygen.

Why other options are wrong:
- Option A: Decay of animals releases carbon dioxide as organic matter decomposes.
- Option B: Respiration releases carbon dioxide as organisms break down glucose for energy.
- Option D: Burning of petrol releases carbon dioxide as hydrocarbons are combusted.

Key Concepts:
- Carbon cycle
- Photosynthesis
- Respiration
- Decomposition
- Combustion

Memory Aids:
- Photosynthesis: CO2 IN, O2 OUT
- Respiration: O2 IN, CO2 OUT

Quick Tips:
- Remember the basic equations for photosynthesis and respiration.

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Lead exhausted in the atmosphere by automobiles using leaded petrol (i.e., tetraethyl lead for improving octane number) is a lethal air pollutant, which causes:

View answer and explanation

Correct option: D

All of the above

Option D (All of the above) is correct because lead exposure can cause paralysis, nervous depression, gastritis, and diarrhea.

Solution approach

Correct Answer + Core Reason: All of the above. Lead poisoning can cause a variety of health issues.

Step-by-Step Solution:
Step 1: Recall the effects of lead poisoning.
Step 2: Lead is a neurotoxin and can affect various systems in the body.
Step 3: Lead exposure can lead to paralysis, nervous depression, gastritis, and diarrhea.

Why other options are wrong:
- Option A: Paralysis of muscles and loss of appetite: This is a symptom of lead poisoning, but not the only one.
- Option B: Nervous depression: This is a symptom of lead poisoning, but not the only one.
- Option C: Gastritis and diarrhea: This is a symptom of lead poisoning, but not the only one.

Key Concepts:
- Lead poisoning
- Environmental pollution

Memory Aids:
- Remember the broad range of symptoms associated with lead poisoning.

Quick Tips:
- Know the health effects of common pollutants.

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Presence of high concentration of ozone and smog in atmospheric air causes:

View answer and explanation

Correct option: B

Cracking of rubber products

The correct answer is Cracking of rubber products. Ozone is a strong oxidizing agent that attacks the double bonds in rubber, leading to its degradation and cracking.

Solution approach

Correct Answer + Core Reason: Cracking of rubber products. Ozone reacts with the double bonds in rubber, causing it to degrade.

Step-by-Step Solution:

Step 1: Identify the pollutants: High concentrations of ozone and smog are present in the atmospheric air.

Step 2: Understand the properties of ozone: Ozone ( $\mathrm{O}_3$ ) is a strong oxidizing agent.

Step 3: Explain the effect on rubber: Ozone attacks the double bonds in unsaturated polymers like rubber, causing chain scission and cracking.

Step 4: Consider the other options:
- Paper embrittlement: While pollutants can affect paper, ozone's primary effect is on rubber.
- Fading of dyes: Pollutants can fade dyes, but ozone's effect on rubber is more significant.
- Damage to electrical insulators: While pollutants can damage insulators, ozone's effect on rubber is more direct and pronounced.

Step 5: Conclude the primary effect: The primary effect of high ozone concentration is the cracking of rubber products.

Why other options are wrong:
- Option A: Embrittlement and decrease of folding resistance of paper: While air pollutants can affect paper, ozone's primary impact is on rubber due to its chemical reactivity with the double bonds in rubber polymers.
- Option C: Fading of dye on textiles: While ozone can contribute to dye fading, its effect on rubber is more significant and direct.
- Option D: Damage of electrical insulator on high tension power line: While pollutants can damage insulators, ozone's effect on rubber is more direct and pronounced.

Key Concepts:
- Ozone as a pollutant
- Oxidation of rubber
- Polymer degradation

Memory Aids:
- Ozone cracks rubber.

Quick Tips:
- Remember that ozone is a strong oxidizing agent that attacks double bonds, especially in rubber.

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The depletion of ozone layer in the stratosphere would lead to:

View answer and explanation

Correct option: D

All of the above

Option D (All of the above) is correct because ozone layer depletion leads to increased UV radiation reaching the Earth's surface, causing cataracts, skin cancer, damage to marine life (plankton), and harm to plants and crops.

Solution approach

Correct Answer + Core Reason: All of the above. Ozone depletion leads to increased UV radiation, causing various harmful effects.

Step-by-Step Solution:

Step 1: Understand the role of the ozone layer. The ozone layer in the stratosphere absorbs harmful ultraviolet (UV) radiation from the sun.

Step 2: Explain the consequences of ozone depletion. Depletion of the ozone layer allows more UV radiation to reach the Earth's surface.

Step 3: Describe the effects of increased UV radiation.
- Increased human cataracts and skin cancer: UV radiation damages DNA and proteins, increasing the risk of these health problems.
- Reduction of plankton in ocean water: UV radiation inhibits photosynthesis in plankton, disrupting marine food chains.
- Depletion of plants and crops: UV radiation damages plant tissues and reduces crop yields.

Step 4: Conclude that all the given options are consequences of ozone depletion.

Why other options are wrong:
- Option A: Increased human cataracts and skin cancer: This is a direct consequence of increased UV radiation, but it's not the only one.
- Option B: Reduction of planktons in ocean water: This is another consequence of increased UV radiation, but it's not the only one.
- Option C: Depletion of plants and crops: This is also a consequence of increased UV radiation, but it's not the only one.

Key Concepts:
- Ozone layer
- UV radiation
- Environmental effects

Memory Aids:
- Ozone protects us from UV radiation.

Quick Tips:
- Remember the harmful effects of UV radiation on living organisms.

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Nitrolium is

View answer and explanation

Correct option: C

{CaCN}_2+{C}

Option C (

{CaCN}_2+{C}

) is correct because Nitrolium is a mixture of calcium cyanamide and carbon.

Solution approach

Correct Answer + Core Reason: ${CaCN}_2+{C}$ . Nitrolium is a fertilizer composed of calcium cyanamide and carbon.

Step-by-Step Solution:
Step 1: Define Nitrolium.
Step 2: Recall the composition of Nitrolium. Nitrolium is a mixture of calcium cyanamide ( ${CaCN}_2$ ) and carbon (C).
Step 3: Understand its use as a fertilizer. It reacts with water to form ammonia, which is vital for plants: ${CaCN}_2+3 {H}_2 {O} \longrightarrow {CaCO}_3+2 {NH}_3$

Why other options are wrong:
- Option A: ${CaCN}_2$ is calcium cyanamide, but Nitrolium is a mixture with carbon.
- Option B: ${Ca}({CN})_2$ is calcium cyanide, which is not Nitrolium.
- Option D: ${Ca}{\left({NO}_3\right)}_2$ is calcium nitrate, which is a different fertilizer.

Key Concepts:
- Fertilizers
- Calcium cyanamide
- Nitrolium composition

Memory Aids:
- Nitrolium contains nitrogen, which is essential for plant growth.

Quick Tips:
- Remember the composition of common fertilizers.

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Photochemical smog is a secondary pollutant and it is generally formed

View answer and explanation

Correct option: B

Around mid day in summer months

Option B (Around mid day in summer months) is correct because photochemical smog formation requires sunlight and high temperatures, which are most prevalent around midday during summer.

Solution approach

Correct Answer + Core Reason: Around mid day in summer months. Photochemical smog requires sunlight and high temperatures for its formation.

Step-by-Step Solution:

Step 1: Define photochemical smog. Photochemical smog is a type of air pollution formed when sunlight reacts with nitrogen oxides and volatile organic compounds (VOCs) in the atmosphere.

Step 2: Identify the necessary conditions for photochemical smog formation:
- Sunlight (UV radiation)
- Nitrogen oxides (NOx)
- Volatile organic compounds (VOCs)
- High temperature

Step 3: Analyze the given options:
- Morning of winters: Low sunlight and temperature, less conducive for smog formation.
- Around mid day in summer months: High sunlight and temperature, ideal for smog formation.
- Rainy day: Reduced sunlight, less conducive for smog formation.
- When the concentration of particulate matter is very low: Particulate matter is not a primary requirement for photochemical smog formation.

Step 4: Conclusion: The conditions for photochemical smog are best met around midday in summer months.

Why other options are wrong:
- Option A: Winter mornings have low sunlight and temperatures, hindering smog formation.
- Option C: Rainy days have reduced sunlight, which is essential for the photochemical reactions.
- Option D: Low particulate matter concentration does not prevent photochemical smog formation; the primary factors are sunlight, NOx, and VOCs.

Key Concepts:
- Photochemical smog
- Air pollution
- Nitrogen oxides
- Volatile organic compounds
- Sunlight

Memory Aids:
- Think of "smog" as needing "sun" and "heat".

Quick Tips:
- Remember that photochemical smog is a secondary pollutant formed by the action of sunlight on primary pollutants.

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Which of the following statements is wrong?

View answer and explanation

Correct option: D

Fishes grow in warm as well as in cold water

Option D (Fishes grow in warm as well as in cold water) is correct because fishes have specific temperature ranges for optimal growth, and not all species can thrive in both warm and cold water.

Solution approach

Correct Answer + Core Reason: Fishes grow in warm as well as in cold water. Fishes have specific temperature ranges for optimal growth, and not all species can thrive in both warm and cold water.

Step-by-Step Solution:

Step 1: Analyze each statement.
- Polar stratospheric clouds (PSCs) are clouds formed over Antarctica: This is true; PSCs form in the extremely cold conditions of the Antarctic stratosphere.
- Acid rain dissolves heavy metals such as $Cu, Pb, Hg$ and $Al$ from soil, rocks and sediments: This is true; acid rain can leach heavy metals from the environment.
- $H_2SO_4$ is major contributor to acid rain, $HNO_3$ ranks second and $HCl$ third in this respect: This is generally true; sulfuric acid is the primary contributor, followed by nitric acid.
- Fishes grow in warm as well as in cold water: This is false; different fish species have different temperature requirements for growth and survival. Warm water holds less dissolved oxygen, which can limit fish growth.

Step 2: Conclusion: The incorrect statement is that fishes grow in warm as well as in cold water.

Why other options are wrong:
- Option A: Polar stratospheric clouds (PSCs) are clouds formed over Antarctica: This is a correct statement.
- Option B: Acid rain dissolves heavy metals such as $Cu, Pb, Hg$ and $Al$ from soil, rocks and sediments: This is a correct statement.
- Option C: $H_2SO_4$ is major contributor to acid rain, $HNO_3$ ranks second and $HCl$ third in this respect: This is a correct statement.

Key Concepts:
- Environmental chemistry
- Acid rain
- Water pollution
- Atmospheric chemistry

Memory Aids:
- Remember the effects of acid rain and the temperature requirements of fish.

Quick Tips:
- Consider the specific environmental conditions and their effects on living organisms.

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It is dangerous to leave the car engine running in a closed garage, because it may cause serious pollution due to poisoning by emission of:

View answer and explanation

Correct option: B

CO

Option B is correct because carbon monoxide (CO) is a highly toxic gas produced by incomplete combustion in car engines. In a closed garage, it can quickly reach dangerous levels, leading to CO poisoning.

Solution approach

Correct Answer + Core Reason: CO. Carbon monoxide is produced by incomplete combustion and is highly toxic.

Step-by-Step Solution:

Step 1: Understand the products of combustion in a car engine.

Step 2: Incomplete combustion produces carbon monoxide (CO), a colorless and odorless gas.

Step 3: Carbon monoxide binds to hemoglobin in the blood more strongly than oxygen, preventing oxygen transport and leading to CO poisoning.

Step 4: In a closed garage, CO can accumulate to dangerous levels quickly.

Why other options are wrong:
- Option A: $\mathrm{C}{\mathrm{O}_2}$ is a greenhouse gas but not as acutely toxic as CO.
- Option C: Unburnt petrol can cause pollution but is not the primary cause of immediate danger in a closed garage.
- Option D: $\mathrm{S}{\mathrm{O}_2}$ is a pollutant but not a major emission from car engines.

Key Concepts:
- Incomplete combustion
- Carbon monoxide poisoning
- Air pollution

Memory Aids:
- CO is a silent killer.

Quick Tips:
- Never run a car engine in a closed space.

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The lowest layer of earth’s atmosphere is

View answer and explanation

Correct option: A

Troposphere

Option A (Troposphere) is correct because the troposphere is the lowest layer of Earth's atmosphere, extending from the surface up to about 10 km.

Solution approach

Correct Answer + Core Reason: Troposphere. The troposphere is the lowest layer of Earth's atmosphere.

Step-by-Step Solution:

Step 1: Recall the layers of Earth's atmosphere in order from lowest to highest.

Step 2: The layers are: Troposphere, Stratosphere, Mesosphere, Thermosphere (including Ionosphere), and Exosphere.

Step 3: Identify the lowest layer.

Step 4: The troposphere is the lowest layer.

Why other options are wrong:
- Option B: The mesosphere is a layer above the stratosphere.
- Option C: The stratosphere is a layer above the troposphere.
- Option D: The ionosphere is a region within the thermosphere, which is a higher layer.

Key Concepts:
- Earth's atmosphere
- Layers of the atmosphere

Memory Aids:
- "The Stratosphere Mesmerizes Tourists In Europe" (Troposphere, Stratosphere, Mesosphere, Thermosphere, Ionosphere, Exosphere).

Quick Tips:
- Know the order of the layers of Earth's atmosphere.

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