Environmental Study Questions in English

(D) Statement $A$ is correct: In the upper stratosphere,$UV$ radiation splits $O_2$ molecules into free oxygen atoms,which then react with $O_2$ to form $O_3$ $(O_2 + O \rightarrow O_3)$.
Statement $B$ is correct: Ozone is a strong oxidizing agent and can oxidize $SO_2$ to $SO_3$ $(O_3 + SO_2 \rightarrow O_2 + SO_3)$.
Statement $C$ is correct: The depletion or thinning of the ozone layer in the stratosphere is commonly referred to as the ozone hole.
Since all statements $A$,$B$,and $C$ are scientifically correct,the correct option is $D$.

(C) Dissolved oxygen is essential for aquatic life.
Organic waste is oxidized by microorganisms using dissolved oxygen.
As a result,the concentration of dissolved oxygen in the water decreases.
This depletion of oxygen is harmful to aquatic life,leading to the death of fishes.

(B) Photochemical smog is oxidizing in nature because it contains a high concentration of oxidizing agents such as $NO_2$ and $O_3$.
Therefore,the statement that it has a low concentration of oxidizing agents is incorrect.

(B) The Earth's atmosphere is divided into different regions such as the troposphere,stratosphere,mesosphere,and thermosphere.
The lowest layer,which extends up to approximately $10 \ km$ from sea level,is known as the Troposphere.

(C) The correct answer is $Peroxyacetyl$ $nitrate$ $(PAN)$.
Primary pollutants are emitted directly from sources into the atmosphere,such as $CO$,$Hydrocarbon$,and $NO$.
Secondary pollutants are formed in the atmosphere through chemical reactions between primary pollutants and other atmospheric components.
$Peroxyacetyl$ $nitrate$ $(PAN)$ is a secondary pollutant formed by the reaction of nitrogen oxides with volatile organic compounds in the presence of sunlight.

(C) The correct answer is that the ozone hole is the thinning of the ozone layer in the stratosphere at some places.
It is not a literal hole,but a significant reduction in the concentration of ozone $(O_3)$ in the stratosphere.
The depletion is primarily caused by compounds like $NO_x$ and $CFCs$ (Chlorofluorocarbons).
The chemical reactions involved are:
$NO_2 + O_3 \rightarrow NO_3 + O_2$
$CF_2Cl_2 \rightarrow CF_2Cl + Cl$
$\dot{Cl} + O_3 \rightarrow Cl\dot{O} + O_2$
$Cl\dot{O} + O \rightarrow \dot{Cl} + O_2$
These reactions occur in the stratosphere.

(D) Green chemistry involves processes and methods that help in minimizing the effects of pollution and eliminating hazardous substances.
It ensures that no products contribute to environmental pollution.
Using plastic cans does not come under green chemistry because plastics are non-biodegradable and contribute to environmental waste.

(A) During lightning in the atmosphere,the high temperature causes nitrogen and oxygen to react to form nitric oxide $(NO)$.
The chemical reaction is: $N_2 + O_2 \rightleftharpoons 2NO$.

(D) $SO_2$ present in the air reacts with water and oxygen to form sulfuric acid.
$2SO_2 + 2H_2O + O_2 \to 2H_2SO_4$
This sulfuric acid damages the calcium in buildings. It is also responsible for causing cough and throat congestion in humans.

(A) In the upper atmosphere,ozone $(O_3)$ is formed by the action of ultraviolet $(UV)$ rays on dioxygen $(O_2)$. The reaction is as follows: $3O_2(g) \xrightarrow{UV} 2O_3(g)$.

(C) Acid rain occurs when the $pH$ of rainwater falls below $5.6$.
The Taj Mahal is made of marble,which is primarily calcium carbonate $(CaCO_3)$.
Acid rain contains sulphuric acid $(H_2SO_4)$,which reacts with the calcium carbonate in the marble to form calcium sulphate $(CaSO_4)$,water,and carbon dioxide.
The reaction is: $CaCO_{3(s)} + H_2SO_{4(aq)} \to CaSO_{4(s)} + H_2O_{(l)} + CO_{2(g)}$.
This process leads to the yellowing and corrosion of the monument's surface.

(A) Methemoglobinemia,commonly known as 'blue baby' syndrome,is caused by the presence of excess nitrate ions in drinking water.
When infants consume water with high nitrate levels,the nitrate is converted to nitrite in the body.
Nitrite reacts with hemoglobin to form methemoglobin,which is unable to transport oxygen effectively,leading to cyanosis (bluish skin discoloration).

(A) Pure water has a $pH$ of $7.0$ (neutral).
Natural,unpolluted rainwater has a $pH$ of about $5.6$ due to the presence of dissolved $CO_{2}$ which forms carbonic acid.
When the $pH$ of rainwater drops below $5.6$,it is termed as acid rain,primarily caused by the presence of atmospheric pollutants like oxides of nitrogen $(NO_{x})$ and sulfur $(SO_{x})$.

(D) Clean water would have a $BOD$ value of less than $5 \ ppm$.
Highly polluted water could have a $BOD$ value of $17 \ ppm$ or more.
Therefore,among the given options,$20 \ ppm$ represents highly polluted water.

(B) pollutant is a substance or energy introduced into the environment that has undesired effects,or adversely affects the usefulness of a resource.
$NO_2$,$O_3$,and hydrocarbons $(C_xH_y)$ are well-known atmospheric pollutants that cause smog and respiratory issues.
$CO_2$ is a natural component of the atmosphere and is essential for photosynthesis in plants.
While high concentrations of $CO_2$ contribute to global warming,it is generally not classified as a pollutant in the same category as toxic gases like $NO_2$ or $O_3$ in standard environmental chemistry contexts.

(A) Pure water has a $pH$ of $7.0$ (neutral).
Natural,unpolluted rainwater has a $pH$ of about $5.6$ due to the presence of dissolved $CO_{2}$.
Acid rain is defined as rainwater with a $pH$ value lower than $5.6$ due to the presence of pollutants like $SO_{2}$ and $NO_{x}$ which form acids in the atmosphere.

(A) Detergents and fertilizers contain phosphates as additives.
The addition of phosphorus into water in the form of the phosphate anion $(PO_{4}^{3-})$ encourages the growth of algae.
This excessive growth of algae reduces the dissolved oxygen concentration in the water,a process known as eutrophication.

(D) Anthropogenic (environmental pollution originating in human activity) sources of water pollution include domestic waste,sewage,soaps,detergents,run-off from agricultural fields having fertilizers and pesticides,industrial wastes as effluents,heat,waste from animal sheds and slaughterhouses,oil spills,etc.

(B) Photochemical smog is formed by the reaction of nitrogen oxides and hydrocarbons in the presence of sunlight.
$PAN$ (Peroxyacetyl nitrate) is a secondary pollutant formed during this process.
It is considered the most harmful component of photochemical smog as it is a powerful eye irritant and is also toxic to plants.

(A) $BOD$ (Biochemical Oxygen Demand) is defined as the amount of dissolved oxygen required by bacteria to decompose the organic matter present in a certain volume of a sample of water.
As the quantity of organic pollutants increases in a water body,the amount of organic matter available for decomposition by microorganisms also increases.
Consequently,microorganisms consume more dissolved oxygen to break down this organic matter,leading to an increase in the $BOD$ value.
Therefore,$BOD$ is directly proportional to the amount of organic pollutants in water.

(B) The presence of excess nitrates $(NO_3^-)$ in drinking water is the primary cause of blue baby syndrome (methemoglobinemia).
When ingested,nitrates are converted into nitrites in the body.
These nitrites react with hemoglobin to form methemoglobin,which is unable to transport oxygen efficiently.
This leads to a lack of oxygen in the blood,causing the skin to appear blue,a condition known as blue baby syndrome.

(D) $DDT$ (Dichlorodiphenyltrichloroethane) is a persistent organic pollutant.
It is non-biodegradable,meaning it does not break down easily in the environment.
Due to its lipophilic nature,it gets stored in the fatty tissues of organisms.
This leads to biomagnification,where the concentration of $DDT$ increases as it moves up the food chain,causing severe ecological damage.

(C) The greenhouse effect occurs when radiation from the sun is trapped within the earth's atmosphere.
The greenhouse effect has been magnified due to the emission of greenhouse gases into the atmosphere by human activities.
Global warming refers to the increase in annual average temperatures across the globe.
As the concentration of greenhouse gases increases,the planet becomes warmer because these gases trap heat in the atmosphere.

(D) Photochemical smog is a type of air pollution that occurs in warm,dry,and sunny climates.
It is formed by the action of sunlight on nitrogen oxides $(NO_x)$ and volatile organic compounds $(VOCs)$ emitted by automobiles and industries.
The reaction produces secondary pollutants like ozone $(O_3)$,formaldehyde,and peroxyacetyl nitrate $(PAN)$.
These pollutants are suspended in the atmosphere and cause respiratory issues,eye irritation,and damage to vegetation.
Therefore,photochemical smog is directly related to air pollution.
Hence,the correct answer is $D$.

(A) Decomposition of organic matter by microbes requires oxygen.
Degree of impurities of water due to organic matter is measured in terms of 'Biological Oxygen Demand' $(BOD)$.
$BOD$ is the oxygen required by microorganisms to metabolise organic wastes.
When sewage is dumped into a river,the amount of organic matter increases,which leads to an increase in the $BOD$ value as more oxygen is consumed by microorganisms for decomposition.

(A) Excess amounts of fluoride in drinking water (above $10 \ ppm$) cause harmful effects to bones and teeth.
This condition is known as fluorosis,which is characterized by the calcification of bones and the mottling of teeth.
Therefore,the correct option is $A$.

(C) Primary pollutants are emitted directly from sources into the atmosphere. Examples include $CO$,$CO_2$,$SO_2$,and hydrocarbons.
Secondary pollutants are not emitted directly but are formed through chemical reactions between primary pollutants and other atmospheric components.
Peroxyacetyl nitrate $(PAN)$ is a classic example of a secondary pollutant formed by the reaction of nitrogen oxides and hydrocarbons in the presence of sunlight.

(C) Greenhouse gases are those that trap heat in the atmosphere,such as $CO_2, CH_4, O_3, N_2O, CFCs,$ and water vapour $(H_2O)$.
$CO$ (carbon monoxide) and $N_2$ (nitrogen) are not considered greenhouse gases.
Therefore,the correct option is $C$.

(D) Water pollution is caused by various contaminants that degrade the quality of water.
$1$. Micro-organisms like bacteria and viruses can contaminate water and cause diseases.
$2$. Organic wastes,such as sewage and agricultural runoff,increase the biochemical oxygen demand $(BOD)$ of water.
$3$. Pesticides and fertilizers from agricultural fields leach into water bodies,causing toxicity and eutrophication.
Since all these factors contribute to water pollution,the correct answer is $D$.

(B) Incomplete combustion of hydrocarbon fuels like petrol or diesel in an automobile engine occurs due to a limited supply of oxygen.
This process primarily produces $CO$ (carbon monoxide) instead of $CO_2$ (carbon dioxide).
Therefore,the presence of $CO$ is the most reliable indicator of incomplete combustion.

(A) Carbon monoxide $(CO)$ has a much higher affinity for hemoglobin than oxygen $(O_2)$.
When $CO$ is inhaled,it binds to hemoglobin to form carboxyhemoglobin $(COHb)$.
This process prevents hemoglobin from transporting oxygen to the body tissues,which can be fatal.

(D) $SO_2$ (Sulfur dioxide) reacts with moisture in the atmosphere to form sulfuric acid,which causes acid rain. Acid rain damages calcium-containing structures like marble $(CaCO_3)$ and limestone. In humans,$SO_2$ is a respiratory irritant that causes cough,throat irritation,and breathlessness.

(D) The ozone layer acts as a shield and prevents harmful ultraviolet $(UV)$ radiation from the sun from reaching the earth.
It does not prevent infrared radiation from reaching the earth.
Therefore,the statement in option $(d)$ is incorrect,making it the correct answer.

(D) Photochemical smog is formed in warm and dry climates due to the action of sunlight on nitrogen oxides and hydrocarbons.
$NO_2$ and $O_3$ are strong oxidizing agents.
They react with unburnt hydrocarbons in the atmosphere to produce secondary pollutants such as formaldehyde,acrolein,and $PAN$ (peroxyacetyl nitrate).
Therefore,$O_3$ and $PAN$ are considered the secondary pollutants or secondary precursors formed during the process.

(C) The irritant red haze observed in traffic and congested urban areas is primarily caused by the presence of oxides of nitrogen $(NO_x)$.
These oxides,particularly nitrogen dioxide $(NO_2)$,contribute to the formation of photochemical smog,which appears as a brownish-red haze.

(B) Photochemical smog is formed by the action of sunlight on nitrogen oxides $(NO_x)$ and hydrocarbons.
Thus,the Assertion is correct.
Vehicular pollution is indeed a major source of nitrogen oxides due to the high-temperature combustion of fuel in engines.
Thus,the Reason is also correct.
However,the Reason does not explain the mechanism of how photochemical smog is produced; it only identifies a source of the pollutant.
Therefore,the Reason is not the correct explanation of the Assertion.

(B) $SPM$ (Suspended Particulate Matter) consists of fine particles floating in the air with a diameter below $10 \ \mu m$. Diesel vehicles are a major source of $SPM$ emissions due to incomplete combustion of fuel. Thus,the Assertion is correct.
Catalytic converters are devices installed in automobiles to reduce the emission of harmful gases like carbon monoxide $(CO)$,hydrocarbons,and nitrogen oxides $(NO_x)$ by converting them into less harmful substances. While they are effective at reducing gaseous pollutants,they do not specifically target $SPM$ (which is particulate matter). Therefore,the Reason is a correct statement,but it does not explain why $SPM$ is released by diesel vehicles. Thus,the correct option is $B$.

(D) Greenhouse gases are gases that trap heat in the atmosphere. The primary greenhouse gases include carbon dioxide $(CO_2)$,methane $(CH_4)$,nitrous oxide $(N_2O)$,water vapour,chlorofluorocarbons $(CFCs)$,and ozone $(O_3)$.
Sulphur dioxide $(SO_2)$ is primarily responsible for acid rain and is not considered a greenhouse gas.

(A) Nitrogen oxides like $NO$ and $NO_2$ are common pollutants produced by both natural processes (e.g.,lightning,forest fires) and human activities (e.g.,combustion in automobile engines). $N_2O$ is primarily produced by natural biological processes in soil and oceans. $N_2O_5$ is not a common pollutant introduced into the atmosphere by these activities.

(D) The greenhouse gases are those that trap heat in the atmosphere.
$CO_2$ (carbon dioxide),$H_2O$ (water vapor),$CFCs$ (chlorofluorocarbons),and $O_3$ (ozone) are known greenhouse gases.
$O_2$ (oxygen) does not contribute to the greenhouse effect.
Therefore,the correct gases are $(a), (b), (c),$ and $(e)$.

(C) Biochemical oxygen demand $(BOD)$ is defined as the amount of dissolved oxygen required by aerobic bacteria to break down the organic matter present in a certain volume of a water sample at a specific temperature over a period of $5$ days.

(N/A) $CO_2$ is an essential gas for life,but its increased concentration in the atmosphere poses a serious threat.
Increased combustion of fossil fuels,decomposition of limestone,and deforestation have led to higher levels of $CO_2$.
$CO_2$ has the property of trapping infrared radiation (heat) emitted by the Earth's surface.
As the concentration of $CO_2$ increases,more heat is trapped in the atmosphere,leading to a rise in global temperatures,a phenomenon known as global warming.

(A) The polluting strength of hydrocarbon fuels depends on the completeness of combustion and the presence of impurities.
$1$. $CNG$ (Compressed Natural Gas) is the cleanest fuel among these as it burns completely with minimal pollutants.
$2$. $LPG$ (Liquefied Petroleum Gas) is cleaner than liquid fuels like kerosene but produces more pollutants than $CNG$.
$3$. Kerosene is a liquid hydrocarbon fuel that produces more smoke and pollutants compared to gaseous fuels like $LPG$ and $CNG$.
Therefore,the increasing order of polluting strength is: $CNG < LPG < \text{Kerosene}$.

(N/A) Tropospheric pollution is caused by the presence of undesirable solid or gaseous particles in the lowest layer of the atmosphere. The main gaseous pollutants include oxides of sulphur ($SO_{2}$,$SO_{3}$),nitrogen ($NO$,$NO_{2}$),and carbon ($CO$,$CO_{2}$),along with hydrocarbons.
Oxides of sulphur and nitrogen are produced by burning fossil fuels. They react with atmospheric oxygen and water to form sulphuric acid $(H_{2}SO_{4})$ and nitric acid $(HNO_{3})$,leading to acid rain,which damages vegetation and buildings.
$2SO_{2(g)} + O_{2(g)} + 2H_{2}O_{(l)} \rightarrow 2H_{2}SO_{4(aq)}$
$4NO_{2(g)} + O_{2(g)} + 2H_{2}O_{(l)} \rightarrow 4HNO_{3(aq)}$
Carbon monoxide $(CO)$ is highly toxic as it binds to hemoglobin,while carbon dioxide $(CO_{2})$ contributes to global warming. Particulate pollutants like dust,mist,and smog also cause respiratory diseases.

(N/A) The major greenhouse gases are:
$1)$ Carbon dioxide $(CO_2)$
$2)$ Methane $(CH_4)$
$3)$ Water vapor $(H_2O)$
$4)$ Nitrous oxide $(N_2O)$
$5)$ Ozone $(O_3)$
$6)$ Chlorofluorocarbons $(CFCs)$

(N/A) Acid rain is a byproduct of various human activities that leads to the emission of oxides of sulphur and nitrogen in the atmosphere. These oxides undergo oxidation and then react with water vapour to form acids.
$2SO_{2(g)} + O_{2(g)} + 2H_2O_{(l)} \longrightarrow 2H_2SO_{4(aq)}$
$4NO_{2(g)} + O_{2(g)} + 2H_2O_{(l)} \longrightarrow 4HNO_{3(aq)}$
Acid rain causes damage to buildings and structures made of stone and metal. In India,limestone is a major stone used in the construction of various monuments and statues,including the Taj Mahal. Acid rain reacts with limestone as:
$CaCO_3 + H_2SO_4 \longrightarrow CaSO_4 + H_2O + CO_2$
This reaction results in the loss of lustre and colour of monuments,leading to their disfiguration.

(N/A) Smog is a form of air pollution resulting from the combination of smoke and fog. There are two primary types of smog:
$a)$ Classical smog
$b)$ Photochemical smog
The differences between the two are summarized in the table below:

Feature	Classical smog vs. Photochemical smog
Occurrence	Classical smog: Occurs in cool,humid climates. Photochemical smog: Occurs in dry,sunny climates.
Components	Classical smog: Smoke,fog,and $SO_2$. Photochemical smog: $PAN$,acrolein,$O_3$,formaldehyde,and $NO$.
Nature	Classical smog: Reducing in nature. Photochemical smog: Oxidizing in nature.

(N/A) Photochemical smog is formed as a result of the reaction of sunlight with hydrocarbons and nitrogen oxides. Ozone,nitric oxide,acrolein,formaldehyde,and peroxyacetyl nitrate $(PAN)$ are common components of photochemical smog. The formation of photochemical smog can be summarized as follows:
Burning of fossil fuels leads to the emission of hydrocarbons and nitrogen dioxide in the atmosphere. High concentrations of these pollutants in air result in their interaction with sunlight as follows:
$NO_{2(g)} \xrightarrow{hv} NO_{(g)} + O_{(g)}$
$O_{(g)} + O_{2(g)} \leftrightarrow O_{3(g)}$
$O_{3(g)} + NO_{(g)} \to NO_{2(g)} + O_{2(g)}$
While ozone is toxic in nature,both $NO_{2}$ and $O_{3}$ are oxidizing agents. They react with the unburnt hydrocarbons in air to produce formaldehyde,$PAN$,and acrolein.
$3CH_{4} + 2O_{3} \to 3CH_{2}O + 3H_{2}O$

(N/A) In the stratosphere,ozone is formed by the action of $UV$ radiation on dioxygen as:
$(i) \, O_{2(g)} \xrightarrow{UV} O_{(g)} + O_{(g)}$
$(ii) \, O_{2(g)} + O_{(g)} \rightarrow{UV} O_{3(g)}$
Reaction $(ii)$ indicates the dynamic equilibrium existing between the production and decomposition of ozone molecules. Any factor that disturbs this equilibrium may cause depletion of the ozone layer. One such factor is the release of chlorofluorocarbon compounds $(CFCs)$. These are non-reactive,non-flammable molecules used in refrigerators,air conditioners,plastics,and electronic industries.
Once released,$CFCs$ mix with atmospheric gases and reach the stratosphere,where they are decomposed by $UV$ radiation:
$(iii) \, CF_{2}Cl_{2(g)} \xrightarrow{UV} \dot{Cl}_{(g)} + \dot{C}F_{2}Cl_{(g)}$
The chlorine free radical produced in reaction $(iii)$ reacts with ozone as:
$(iv) \, \dot{Cl}_{(g)} + O_{3(g)} \to Cl\dot{O}_{(g)} + O_{2(g)}$
$(v) \, Cl\dot{O}_{(g)} + O_{(g)} \to \dot{Cl}_{(g)} + O_{2(g)}$
The regeneration of $\dot{Cl}_{(g)}$ radicals causes a continuous breakdown of ozone present in the stratosphere,leading to the depletion of the ozone layer.

In polar regions,stratospheric clouds provide the surface for chlorine nitrate and hypochlorous acid,which react further to give molecular chlorine. Molecular chlorine and $HOCl$ are photolysed to give chlorine-free radicals.
$ClONO_{2(g)} + H_2O_{(g)} \to HOCl_{(g)} + HNO_{3(g)}$
$ClONO_{2(g)} + HCl_{(g)} \to Cl_{2(g)} + HNO_{3(g)}$
$HOCl_{(g)} \xrightarrow{hv} \dot{O}H_{(g)} + \dot{Cl}_{(g)}$
$Cl_{2(g)} \xrightarrow{hv} \dot{Cl}_{(g)} + \dot{Cl}_{(g)}$
The chlorine-free radicals lead to the decomposition of ozone as:
$\dot{Cl}_{(g)} + O_{3(g)} \to Cl\dot{O}_{(g)} + O_{2(g)}$
Hence,a chain reaction is initiated. The chlorine-free radical is continuously regenerated,thereby depleting the ozone layer. This phenomenon is known as the 'ozone hole'.
Effects of depletion of the ozone layer:
The ozone layer protects the Earth from the harmful $UV$ radiations of the sun. With the depletion of the layer,more radiation enters the Earth's atmosphere. $UV$ radiations are harmful because they lead to the ageing of skin,cataracts,skin cancer,and sunburns. They cause the death of many phytoplanktons,which leads to a decrease in fish productivity. Excess exposure may even cause mutations in plants.
An increase in $UV$ radiations decreases the moisture content of the soil and damages both plants and fibers.