Environmental Study Questions in English

(A) The thermosphere is the fourth layer of the Earth's atmosphere and is located above the mesosphere.
In this region,the air is very thin.
The thermosphere includes the ionosphere,which is a region filled with charged particles.
Due to high temperatures and solar radiation,molecules undergo ionization to form species such as $O_2^{+}$,$O^{+}$,and $NO^{+}$.

(C) The depletion of the ozone layer in the stratosphere is primarily caused by substances that release chlorine or bromine radicals,such as chlorofluorocarbons $(CF_2Cl_2)$ and nitrogen oxides $(NO)$.
$Cl_2$ can also contribute to ozone depletion through the release of chlorine atoms.
$CH_4$ (methane) is a greenhouse gas,but it is not primarily responsible for the depletion of the ozone layer; in fact,it can react with chlorine radicals to form $HCl$,which helps in the removal of ozone-depleting chlorine species.

(A) $I$. Photochemical smog is formed by the action of sunlight on nitrogen oxides and hydrocarbons,resulting in a high concentration of oxidizing agents like $O_3$ and $PAN$. This statement is correct.
$II$. Classical smog is a mixture of smoke,fog,and $SO_2$ (reducing smog),not $NO_2$. This statement is incorrect.
$III$. High concentrations of $SO_2$ lead to the stiffness of flower buds,which eventually fall off from plants. This statement is correct.
$IV$. Normal rain water has a pH of approximately $5.6$ due to the dissolution of atmospheric $CO_2$. $A$ pH of $7.5$ is incorrect. This statement is incorrect.
Therefore,statements $I$ and $III$ are correct.

(D) $NO_2$ (nitrogen dioxide) is a well-known lung irritant.
High concentrations of $NO_2$ can lead to the damage of the leaves of plants and retard the rate of photosynthesis.
It is a toxic gas to both plants and animals.
In humans,$NO_2$ is a respiratory irritant that can cause acute respiratory diseases in children,such as bronchitis and damage to the lungs.

(D) Photochemical smog is formed by the action of sunlight on nitrogen oxides $(NO_x)$ and hydrocarbons.
Common components of photochemical smog include ozone $(O_3)$,nitric oxide $(NO)$,formaldehyde $(HCHO)$,acrolein $(CH_2=CH-CHO)$,and peroxyacetyl nitrate $(PAN)$.
Sulphur dioxide $(SO_2)$ is a primary component of classical smog (reducing smog),not photochemical smog (oxidizing smog).
Therefore,$SO_2$ is not a common component of photochemical smog.

(C) Statement-$I$: Photochemical smog is formed by the action of sunlight on nitrogen oxides and hydrocarbons. Common components include acrolein $(CH_2=CHCHO)$,formaldehyde $(HCHO)$,and peroxyacetyl nitrate $(PAN)$. Thus,Statement-$I$ is correct.
Statement-$II$: Greenhouse gases trap heat in the atmosphere. From the list $(CH_4, CO_2, NO, H_2O_{(l)}, H_2O_{(g)}, O_2, O_3)$,the greenhouse gases are $CH_4$,$CO_2$,$H_2O_{(g)}$,and $O_3$. Note that $NO$ is not a significant greenhouse gas,$O_2$ is not a greenhouse gas,and $H_2O_{(l)}$ (liquid water) is not considered a greenhouse gas in this context. The count is $4$,not $5$. Thus,Statement-$II$ is incorrect.

(D) Photochemical smog is formed by the action of sunlight on nitrogen oxides $(NO_x)$ and volatile organic compounds $(VOCs)$ in the atmosphere.
Its common components include Ozone $(O_3)$,Nitrogen dioxide $(NO_2)$,Peroxyacetyl nitrate $(PAN)$,and aldehydes (compounds containing the $-CHO$ group).

(A) Ozone is formed in the stratosphere by the action of $UV$ radiation on dioxygen molecules. The $UV$ radiation splits the $O_2$ molecule into two nascent oxygen atoms. These nascent oxygen atoms then react with other $O_2$ molecules to form ozone $(O_3)$. The reactions are as follows:
$O_2 \xrightarrow[\lambda < 242.5 \ nm]{UV \ Radiation} O + O$
$O_2 + O \rightarrow O_3 \ (\text{Ozone})$

(B) Global warming refers to the steady temperature rise on our planet. It is the unusually rapid increase in Earth's average surface temperature over the past century,primarily due to greenhouse gases released by burning fossil fuels.
One of the major consequences of global warming is the melting of Himalayan glaciers,as glacier ice loss is directly linked to rising global temperatures.

(C) Photochemical smog is formed by the action of sunlight on nitrogen oxides $(NO_x)$ and volatile organic compounds $(VOCs)$.
It typically contains $NO_2$,$O_3$,formaldehyde,acrolein,and peroxyacetyl nitrate $(PAN)$.
$SO_2$ is a primary component of classical (sulfurous) smog,not photochemical smog.
Therefore,$SO_2$ is not a component of photochemical smog.

(D) Oxides of sulphur are major air pollutants. For example,$H_2S$ is readily oxidised to $SO_2$ in the atmosphere.
$2H_2S + 3O_2 \rightarrow 2SO_2 + 2H_2O$
$H_2S + O_3 \rightarrow SO_2 + H_2O$
Thus,oxides of sulphur like $SO_2$ are significant contributors to air pollution.

(B) Photochemical smog is a type of smog produced when ultraviolet light from the sun reacts with nitrogen oxides in the atmosphere.
It is visible as a brown haze and is most prominent during the morning and afternoon,especially in densely populated,warm cities.
Photochemical smog is a mixture of ozone,nitric acid,aldehydes,peroxyacyl nitrates $(PAN)$,and other secondary pollutants.
Among the given options,$NO_2$ is a primary precursor and a key component involved in the formation of photochemical smog.
Hence,the correct option is $B$.

(B) Atmospheric residence time is the average time a molecule spends in the atmosphere between its emission from a source and its removal by a sink.
Among the common greenhouse gases,$CH_4$ (Methane) has the shortest atmospheric residence time,typically estimated at approximately $12$ years.
In comparison,$CO_2$ (Carbon dioxide) has a residence time ranging from $50$ to $200$ years,$N_2O$ (Nitrous oxide) is about $114$ years,and $CFCs$ (Freons) can persist for decades to centuries.

(C) Acid rain is primarily caused by the presence of oxides of sulphur and nitrogen in the atmosphere.
These gases,specifically $SO_2$ and $NO_2$,react with water vapor in the atmosphere to form sulphuric acid $(H_2SO_4)$ and nitric acid $(HNO_3)$.
These acids then fall to the Earth's surface as acid rain.
Therefore,the correct combination is $I$ and $III$.

(D) The irritant red haze in traffic and congested places is due to the oxides of nitrogen $(NO_x)$.
Nitrogen dioxide $(NO_2)$ is a poisonous gas with a reddish-brown color.
When it is mixed with aerosols in the atmosphere,it causes a reddish-brown haze in congested areas.
Thus,option $(D)$ is correct.

(C) The reaction sequence shows that $NO$ and $NO_2$ participate in the catalytic cycle that maintains the concentration of $O_3$ in the atmosphere.
The formation of formaldehyde $(H_2C=O)$ from methane $(CH_4)$ is directly dependent on the concentration of ozone $(O_3)$.
Since the concentration of $O_3$ is regulated by the $NO_x$ cycle ($NO$ and $NO_2$),the overall formation of formaldehyde is controlled by the presence of $O_3, NO$ and $NO_2$.
Therefore,option $(C)$ is correct.

(A) Photochemical smog is formed by the reaction of sunlight,nitrogen oxides $(NO_x)$,and volatile organic compounds $(VOCs)$ in the atmosphere.
The primary reactions involved are:
$(I)$ $NO + O_2 \longrightarrow NO_2$
$(II)$ $NO_{2(g)} \stackrel{h \nu}{\longrightarrow} NO_{(g)} + [O]$
$(III)$ $[O] + O_2 \longrightarrow O_3$
$(IV)$ $O_3 + NO \longrightarrow NO_2 + O_2$
$SO_2$ is primarily associated with classical (sulfurous) smog,not photochemical smog.

(A) Photochemical smog is formed by the action of sunlight on nitrogen oxides $(NO_x)$ and hydrocarbons.
Reaction $(ii)$ shows the photolysis of $NO_2$ to produce atomic oxygen,which then reacts with $O_2$ to form ozone $(O_3)$.
Reaction $(iii)$ represents the oxidation of hydrocarbons (like $CH_4$) by ozone to form formaldehyde $(CH_2=O)$ and water.
Reaction $(iv)$ shows the reaction between $NO$ and $O_3$ to regenerate $NO_2$ and $O_2$.
Reaction $(i)$ is not a characteristic reaction of photochemical smog.
Therefore,reactions $(ii)$,$(iii)$,and $(iv)$ are involved in the formation and cycle of photochemical smog.

(B) Photochemical smog is formed due to the presence of nitrogen oxides $(NO_x)$,hydrocarbons,and sunlight.
It is a daytime phenomenon and contains many reactive molecules like ozone $(O_3)$,nitric oxide $(NO)$,and formaldehyde $(HCHO)$.
Statement $(i)$ is correct because photochemical smog is oxidizing in nature due to the presence of ozone and other oxidizing agents.
Statement $(ii)$ is correct as it contains highly reactive species.
Statement $(iii)$ is incorrect because the main components are nitrogen oxides and hydrocarbons,not just oxides of carbon.
Statement $(iv)$ is incorrect because ozone formation is primarily driven by nitrogen oxides and hydrocarbons,not carbon monoxide.

(A) Chlorofluorocarbons (CFCs),also known as freons,are stable,non-toxic,and non-reactive compounds used in refrigeration and air conditioning.
Due to their long atmospheric lifetime,they eventually reach the stratosphere.
In the stratosphere,they are decomposed by high-energy $UV$ radiation,leading to the formation of chlorine free radicals.
The reaction for dichlorodifluoromethane $(CF_2Cl_2)$ is:
$CF_2Cl_2 \stackrel{hv}{\longrightarrow} \dot{C}F_2Cl + \dot{Cl}$
Thus,the products $X$ and $Y$ are the free radicals $\dot{C}F_2Cl$ and $\dot{Cl}$.

(B) The most serious effect of the depletion of the ozone layer is that $UV$ rays from the sun can pass through the stratosphere and reach the surface of the earth.
It has been found that with an increase in exposure to $UV$ rays,the risk of skin cancer increases.
Also,exposure of the eye to $UV$ rays damages the cornea and lens,which may cause cataract and even blindness.

(C) Acid rain is primarily caused by the emission of oxides of nitrogen and sulphur into the atmosphere.
These gases react with water vapor in the atmosphere to form strong acids,namely nitric acid $(HNO_3)$ and sulphuric acid $(H_2SO_4)$,which then fall as acid rain.
The chemical reactions are as follows:
$2NO_2 + H_2O \rightarrow HNO_3 + HNO_2$
$2SO_2 + O_2 + 2H_2O \rightarrow 2H_2SO_4$
Thus,the pair of gases responsible for acid rain is $NO_2$ and $SO_2$.

(C) The Bhopal gas tragedy,which occurred in $1984$,was caused by the accidental release of Methyl isocyanate $(CH_3NCO)$ gas.
Methyl isocyanate is commonly abbreviated as $MIC$.

(A) The acceptable level of carbon monoxide gas $(CO)$ in the atmosphere is approximately $9 \ ppm$.

(D) Chlorofluorocarbons $(CFCs)$ are responsible for the depletion of ozone in the stratosphere.
$CFCl_3$ decomposes in the presence of ultraviolet radiation to produce chlorine free radicals $(Cl^{\bullet})$.
These chlorine free radicals react with ozone $(O_3)$ molecules to form oxygen $(O_2)$ and chlorine monoxide $(ClO^{\bullet})$.
The reaction is: $Cl^{\bullet} + O_3 \rightarrow ClO^{\bullet} + O_2$.

(A) Nitrogen gas $(N_2)$ is the major component of the atmosphere,constituting approximately $78 \%$ by volume.
It is an inert gas under normal conditions and does not cause air pollution.
In contrast,$N_2O$,$NO$,and $CO$ are known air pollutants.

(B) The atmosphere is divided into layers based on altitude from the Earth's surface:
$1$. Troposphere: $0-10 \ km$
$2$. Stratosphere: $10-50 \ km$
$3$. Mesosphere: $50-85 \ km$
$4$. Thermosphere: $85-500 \ km$
Comparing the altitudes,the order is Thermosphere $(85-500 \ km)$ > Mesosphere $(50-85 \ km)$ > Troposphere $(0-10 \ km)$.
Therefore,the decreasing order of altitude is $III, II, I$.

(D) The depletion of the ozone layer is primarily caused by the release of $Chloro-fluoro \ carbons$ $(CFCs)$.
These compounds,when released into the atmosphere,reach the stratosphere where they are broken down by ultraviolet radiation to release chlorine atoms.
These chlorine atoms then catalyze the destruction of ozone $(O_3)$ molecules into oxygen $(O_2)$.

(B) According to the guidelines for drinking water quality (as per $NCERT$ Chemistry textbook,Environmental Chemistry chapter),the maximum prescribed concentration of copper $(Cu)$ is $3.0 \ mg \ dm^{-3}$.
The maximum prescribed concentration of zinc $(Zn)$ is $5.0 \ mg \ dm^{-3}$.
Given that the concentration of copper is $x = 3.0 \ mg \ dm^{-3}$,we need to find the concentration of zinc in terms of $x$.
Since $Zn = 5.0 \ mg \ dm^{-3}$ and $Cu = 3.0 \ mg \ dm^{-3}$,the ratio is $\frac{Zn}{Cu} = \frac{5}{3}$.
Therefore,$Zn = \frac{5}{3} x$ is not directly listed,but based on standard values provided in the curriculum,the correct value for zinc is $5.0 \ mg \ dm^{-3}$.

(C) Eutrophication is a process where water bodies receive excessive amounts of nutrients,such as nitrates and phosphates,which results in excessive plant and algal growth.
As these plants die and decompose,the process consumes a large amount of oxygen.
Therefore,eutrophication leads to a significant decrease in the level of $DO$ (dissolved oxygen) in the water.

(C) The organic matter present in the water sample is oxidized by potassium dichromate in the presence of $H_2SO_4$ to produce $CO_2$ and $H_2O$.
This reaction helps in the determination of the $COD$ of the water sample.
Therefore,the correct reagent is acidified potassium dichromate.

(A) The amount of oxygen required by bacteria to break down the organic matter present in a certain volume of a sample of water is called biochemical oxygen demand $(BOD)$.
$BOD$ is a measure of the amount of organic material in water in terms of the oxygen required to break it down biologically.
Clean water typically has a $BOD$ value of less than $5 \ ppm$,whereas highly polluted water can have a $BOD$ value of $17 \ ppm$ or more.
Therefore,a $BOD$ value less than $5 \ ppm$ indicates that the water sample is clean and rich in dissolved oxygen.

(A) The $BOD$ (Biochemical Oxygen Demand) is a measure of the amount of dissolved oxygen required by aerobic microorganisms to decompose organic matter present in a given volume of water.
Pure water has a very low $BOD$ value,typically around $1 \ ppm$.
$A$ water supply with a $BOD$ level of $3-5 \ ppm$ is considered moderately clean,while water with a $BOD$ level of $6-9 \ ppm$ is considered polluted.

(B) The amount of oxygen required by bacteria to break down the organic matter present in a certain volume of a sample of water is called biochemical oxygen demand $(BOD)$.
The amount of $BOD$ in the water is a measure of the amount of organic material in water in terms of how much oxygen will be required to break it down biologically.
Clean water has a $BOD$ value of less than $5 \ ppm$,whereas highly polluted water,such as municipal sewage,has a $BOD$ value of more than $100 \ ppm$.

(A) The concentration of dissolved oxygen $(D.O.)$ in water is a key indicator of water quality.
According to environmental standards,water is considered to be polluted if the $D.O.$ content is less than $5 \ ppm$.
If the $D.O.$ value is below $5 \ ppm$,it indicates that the water is not suitable for the survival of aquatic life.

(D) The correct matches are as follows:
$(A)$ Bleaching of paper $\rightarrow$ $(II)$ $H_2O_2$ is used as a bleaching agent for paper.
$(B)$ Eye irritant $\rightarrow$ $(IV)$ $PAN$ (Peroxyacetyl nitrate) is a well-known eye irritant.
$(C)$ Freons $\rightarrow$ $(I)$ $CF_2Cl_2$ (Dichlorodifluoromethane) is a common type of freon.
$(D)$ Herbicide $\rightarrow$ $(III)$ $Na_2AsO_3$ (Sodium arsenite) is used as an herbicide.
Therefore,the correct sequence is $A-II, B-IV, C-I, D-III$.
Hence,option $(D)$ is the correct answer.

(B) Acrolein is an unsaturated aldehyde with the chemical formula $CH_2=CH-CHO$.
It is formed as a byproduct of photochemical smog reactions involving unburnt hydrocarbons,nitrogen oxides $(NO_x)$,and ozone $(O_3)$ in the atmosphere.
The reaction products typically include formaldehyde $(CH_2=O)$,acrolein $(CH_2=CH-CHO)$,and peroxyacetyl nitrate $(CH_3CO(OO)NO_2)$.

(A) Carboxyhaemoglobin is a stable complex of carbon monoxide and haemoglobin that forms in red blood cells upon contact with carbon monoxide.
When the concentration of carboxyhaemoglobin in the blood reaches $3-4 \%$,it reduces the oxygen-carrying capacity of the blood.
This condition leads to symptoms such as headache,increased stress on the heart,and cardiovascular problems.
Therefore,statements $(I)$ and $(II)$ are correct.

(A) Carbon monoxide $(CO)$ binds with $Fe(II)$ of haemoglobin to form a stable carboxyhaemoglobin complex.
This complex is about $300$ times more stable than the oxygen-haemoglobin complex.
Therefore,the presence of $CO$ inhibits the transport of $O_2$ by haemoglobin,leading to a toxic effect.

(C) $1$. $SO_2$: Acid rain. Nitrogen oxides and sulphur dioxide react with water droplets in clouds to form sulphuric and nitric acids,resulting in acid rain.
$2$. $PAN$: Photochemical smog. Peroxyacetyl nitrate $(PAN)$ is a phytotoxic air pollutant formed by the reaction of hydrocarbons and nitrogen oxides in the presence of sunlight.
$3$. Smoke: Particulate. Smoke consists of a mixture of solid particles and liquid droplets suspended in the air.
$4$. $CF_2Cl_2$: Stratospheric pollutant. Chlorofluorocarbons like $CF_2Cl_2$ are responsible for the depletion of the ozone layer in the stratosphere.