Ozone Depletion in the Stratosphere Questions in English

(C) The ozone layer is a region of the Earth's stratosphere that absorbs most of the Sun's ultraviolet $(UV)$ radiation.
It contains a high concentration of ozone $(O_3)$ in relation to other parts of the atmosphere.
The stratosphere is located above the troposphere and extends from about $10 \ km$ to $50 \ km$ above the Earth's surface.
Therefore,the correct option is $C$.

(A) The ozone layer in the stratosphere acts as a shield by absorbing harmful ultraviolet $(UV)$ radiation from the sun.
Depletion of the ozone layer allows more $UV-B$ radiation to reach the Earth's surface.
Increased exposure to $UV-B$ radiation causes $DNA$ damage and mutations in skin cells,which leads to an increased incidence of skin cancer and other skin-related disorders.

(C) World Ozone Day is celebrated annually on $16th$ September.
This date was designated by the United Nations General Assembly to commemorate the signing of the Montreal Protocol on Substances that Deplete the Ozone Layer in $1987$.
The primary objective of this day is to raise awareness about the importance of the ozone layer and the need to protect it from ozone-depleting substances.

(D) In the stratosphere,chlorofluorocarbons $(CFCs)$ are broken down by ultraviolet $(UV)$ radiation,which releases chlorine atoms $(Cl)$.
These chlorine atoms act as catalysts in the degradation of ozone $(O_3)$ into molecular oxygen $(O_2)$.
The reaction mechanism is as follows:
$Cl + O_3 \rightarrow ClO + O_2$
$ClO + O \rightarrow Cl + O_2$
Thus,the chlorine atom is regenerated and continues to destroy more ozone molecules.

(A) The $Montreal$ protocol was signed in $1987$ to control the emission of ozone-depleting substances,specifically chlorofluorocarbons $(CFCs)$.
This international treaty was designed to protect the ozone layer by phasing out the production and consumption of numerous substances that are responsible for ozone depletion.
In contrast,the $Kyoto$ protocol was focused on reducing greenhouse gas emissions to combat global warming.

(C) The Montreal Protocol $(1987)$ was a landmark international agreement designed to protect the stratospheric ozone layer.
It achieved this by establishing regulations to limit the production and consumption of ozone-depleting substances,such as chlorofluorocarbons $(CFCs)$.

(C) The stratosphere contains the ozone layer,which is primarily located between $15\, km$ and $30\, km$ above the Earth's surface.
This layer is often referred to as the ozonosphere.
Ozone molecules in this region absorb harmful ultraviolet $(UV)$ radiation from the sun,protecting life on Earth.
The temperature in the stratosphere increases with altitude due to the absorption of $UV$ radiation by ozone.
Chemical reactions involving nitrogen oxides and hydrocarbons in the presence of $UV$ rays lead to the formation of ozone $(O_3)$ and other pollutants like peroxyacetyl nitrate $(PAN)$.

(C) In the environment,ozone is known for both its harmful and useful effects.
Ozone present in the stratosphere is useful because it acts as a shield and protects the Earth from harmful $UV$ rays.
Ozone present in the troposphere acts as a pollutant and has many deleterious effects on living organisms.

(C) The Assertion is correct: In the stratosphere,$UV$ radiation causes the photodissociation of ozone $(O_3)$ into molecular oxygen $(O_2)$ and atomic oxygen $(O)$. This is a natural process,but the depletion of the ozone layer is primarily accelerated by chlorofluorocarbons $(CFCs)$.
The Reason is incorrect: The ozone hole refers to the thinning of the stratospheric ozone layer,which leads to increased $UV$ radiation reaching the Earth's surface,causing skin cancer,cataracts,and damage to $DNA$. While ozone depletion is a serious environmental issue,it is not the primary cause of global warming or climate change; global warming is primarily caused by the greenhouse effect due to the accumulation of greenhouse gases like $CO_2$,$CH_4$,and $N_2O$.

(C) The stratosphere of the Earth's atmosphere contains an ozone layer that protects us from harmful ultraviolet $(UV)$ radiations from the sun.
Chlorofluorocarbons $(CFCs)$,which contain chlorine,are used as coolants in air conditioners and refrigerators and are the primary chemicals responsible for ozone depletion.
After being released into the troposphere,$CFCs$ migrate to the stratosphere,where they are broken down by $UV$ radiation,releasing chlorine atoms.
In the presence of sunlight,these chlorine atoms break down $O_3$ into $O_2$.
While the Assertion is correct,the statement that the ozone level decreases by $67\%$ every year is factually incorrect,as the depletion rate is not a fixed annual percentage of $67\%$ globally.
Therefore,the Assertion is correct,but the Reason is incorrect.

(D) Ozone is found in two layers of the atmosphere: the troposphere and the stratosphere.
$1$. Stratospheric ozone is considered 'good' ozone because it forms a layer that absorbs harmful $UV$ radiations from the sun,protecting living organisms on Earth.
$2$. Tropospheric ozone is considered 'bad' ozone because it is a pollutant at ground level,formed by the reaction of nitrogen oxides and volatile organic compounds in the presence of sunlight,and it can be harmful to human health and plants.
Therefore,the statement that stratospheric ozone protects us from $UV$ radiations is correct.

(N/A) The ozone hole is most prominent over the Antarctica region. It is formed due to the increased concentration of chlorine in the atmosphere.
Chlorine is primarily released from chlorofluorocarbons $(CFCs)$ which are widely used as refrigerants. These $CFCs$ migrate from the troposphere to the stratosphere,where they release chlorine atoms through the action of $UV$ rays. The released chlorine atoms catalyze the conversion of ozone $(O_3)$ into molecular oxygen $(O_2)$. $A$ single atom of chlorine can destroy approximately $10,000$ molecules of ozone,leading to significant ozone depletion.
The formation of the ozone hole results in an increased intensity of $UV-B$ radiation reaching the Earth's surface. $UV-B$ radiation damages $DNA$ and accelerates skin ageing. It also causes skin darkening and increases the risk of skin cancer. Furthermore,high levels of $UV-B$ exposure can cause corneal cataracts in human beings.

(D) The ozone found in the lower atmosphere (troposphere) is considered 'bad' ozone as it harms plants and animals. The 'good' ozone is found in the upper atmosphere,known as the stratosphere,which acts as a shield by absorbing ultraviolet $(UV)$ radiation from the sun. $UV$ rays are highly damaging to organisms because they are absorbed by $DNA$ and proteins,causing their chemical bonds to break. The thickness of the ozone layer in a column of air from the ground to the top of the atmosphere is measured in Dobson units $(DU)$. Ozone is continuously produced by the action of $UV$ rays on molecular oxygen $(O_2)$ and simultaneously degraded into molecular oxygen in the stratosphere. There should be a balance between production and degradation of ozone in the stratosphere. However,this balance has been disrupted due to the enhancement of ozone degradation by chlorofluorocarbons (CFCs). CFCs are widely used as refrigerants. When CFCs released from the lower atmosphere reach the stratosphere,$UV$ rays act on them,releasing chlorine atoms. These chlorine atoms degrade ozone into molecular oxygen,leading to the thinning of the ozone layer,commonly referred to as the 'ozone hole'. The Montreal Protocol was signed in Montreal,Canada,in $1987$ (effective in $1989$) to control the emission of ozone-depleting substances,especially CFCs,to protect the ozone layer.

(N/A) $(i)$ Snow blindness: It is a painful condition of the eyes caused by high exposure to ultraviolet-$B$ $(UV-B)$ radiation. The $UV-B$ radiation causes inflammation of the cornea,which leads to temporary blindness.
$(ii)$ Ozone hole: It refers to the significant thinning of the ozone layer in the stratosphere,particularly over the Antarctica region. This depletion is primarily caused by the release of chlorofluorocarbons $(CFCs)$ into the atmosphere,which react with ozone $(O_3)$ and break it down into oxygen $(O_2)$.

(N/A) The depletion of the ozone layer in a restricted area is known as an ozone hole. It was first discovered over Antarctica. The air over Antarctica is isolated from the rest of the world by a phenomenon called the polar vortex. $CFCs$ released into the atmosphere gradually reach the stratosphere,and winds transport them toward the polar regions. The atmospheric conditions prevailing in Antarctica during winter months facilitate the formation of the ozone hole. The lack of sunlight and extremely low temperatures during winter lead to the formation of ice clouds,which provide a catalytic surface for chlorine reactions. $UV-B$ radiation is highly harmful. The cornea of the human eye absorbs $UV-B$ radiation,and a high dose of this radiation causes inflammation of the cornea,a condition called 'snow blindness' or cataract,which can lead to permanent damage to the cornea. $UV-B$ radiation also damages skin cells and causes skin cancer.

(C) The Montreal Protocol is an international treaty designed to protect the ozone layer by phasing out the production and consumption of numerous substances that are responsible for ozone depletion. It was signed in $1987$ and came into force in $1989$. These substances include chlorofluorocarbons $(CFCs)$ and other ozone-depleting substances $(ODS)$.

(B) The Montreal Protocol is an international treaty designed to protect the ozone layer by phasing out the production and consumption of numerous substances that are responsible for ozone depletion. It was signed in $1987$ and came into force in $1989$. The primary substances targeted are chlorofluorocarbons $(CFCs)$ and other ozone-depleting substances $(ODS)$.

(D) The ozone layer,composed of $O_3$ (ozone) molecules,is located in the stratosphere.
It acts as a protective shield by absorbing the majority of harmful ultraviolet $(UV)$ radiation emitted by the sun.
This prevents $UV$ rays from reaching the Earth's surface,thereby protecting living organisms from potential damage such as skin cancer and cataracts.

(D) The thickness of the ozone layer in a column of air from the ground to the top of the atmosphere is measured in terms of Dobson units $(DU)$.
One Dobson unit is equivalent to a layer of pure ozone $0.01 \ mm$ thick at standard temperature and pressure $(STP)$.

(B) The atmosphere is divided into several layers based on temperature and composition.
The $O_3$ (ozone) layer is primarily located in the stratosphere,which extends from approximately $10 \ km$ to $50 \ km$ above the Earth's surface.
This layer is known as the 'good ozone' layer because it absorbs the harmful ultraviolet $(UV)$ radiation emitted by the Sun,protecting living organisms on Earth from its damaging effects.

(C) $CFCs$ stands for Chlorofluorocarbons.
These are organic compounds that contain carbon,chlorine,and fluorine.
They were widely used as refrigerants,propellants in aerosols,and solvents.
Due to their stability,they reach the stratosphere where they break down and release chlorine atoms,which deplete the ozone layer.

(B) The depletion of the ozone layer is primarily caused by chlorofluorocarbons $(CFCs)$.
When $CFCs$ reach the stratosphere,they are broken down by ultraviolet $(UV)$ radiation,releasing chlorine atoms $(Cl)$.
These chlorine atoms act as catalysts in the breakdown of ozone $(O_3)$ into oxygen $(O_2)$,leading to the thinning of the ozone layer.

(D) In the stratosphere,ultraviolet $(UV)$ rays act on molecular oxygen $(O_2)$ to split it into free oxygen atoms $(O + O)$.
These free oxygen atoms then combine with molecular oxygen $(O_2)$ to form ozone $(O_3)$.
This process is essential for the formation of the ozone layer,which protects the Earth from harmful $UV$ radiation.
Therefore,the action of $UV$ rays on molecular oxygen leads to the formation of ozone in the stratosphere.

(A) The depletion of the ozone layer is primarily caused by the release of chlorofluorocarbons $(CFCs)$.
$CFCs$ are used as refrigerants in air conditioners and refrigerators.
When $CFCs$ reach the stratosphere,they are broken down by ultraviolet $(UV)$ radiation,releasing chlorine atoms.
These chlorine atoms act as catalysts in the breakdown of ozone $(O_3)$ into oxygen $(O_2)$,leading to the thinning of the ozone layer.

(B) The ozone hole is a region of exceptionally depleted ozone in the stratosphere over the Antarctic. It was first discovered in the $1980s$ by scientists. The depletion is primarily caused by the release of chlorofluorocarbons $(CFCs)$ and other ozone-depleting substances. Therefore,the correct option is $B$ (Antarctica).

(A) The $Montreal$ $Protocol$ was signed in $1987$ in $Montreal$,$Canada$,to control the emission of ozone-depleting substances $(ODS)$ such as chlorofluorocarbons $(CFCs)$.
Its primary objective is to protect the stratospheric ozone layer from depletion.
Therefore,the correct option is $A$.

(A) Ozone is found in two layers of the atmosphere: the stratosphere and the troposphere.
$1$. The ozone found in the stratosphere is called 'good ozone' because it acts as a shield,absorbing harmful ultraviolet $(UV)$ radiation from the sun.
$2$. The ozone found in the troposphere is called 'bad ozone' because it is a pollutant that is harmful to plants and animals,including humans,as it triggers breathing problems and damages the respiratory system.
Therefore,the correct option is $A$.

(B) The $Montreal$ $Protocol$ was an international treaty designed to protect the ozone layer by phasing out the production and consumption of numerous substances that are responsible for ozone depletion.
It was signed in $1987$ and came into force in $1989$.
The primary substances targeted are chlorofluorocarbons $(CFCs)$ and other related chemicals.
Therefore,the correct purpose is the control of emission of ozone-depleting substances.

(C) Let's analyze each statement:
$(i)$ The Montreal Protocol was indeed signed in $1987$ to control the emission of ozone-depleting substances and became effective in $1989$. This is correct.
$(ii)$ 'Good' ozone is found in the stratosphere,not the troposphere. The troposphere contains 'bad' ozone. This is incorrect.
$(iii)$ Ozone is formed by the action of $UV$ rays on molecular oxygen $(O_2)$ in the stratosphere,and it also degrades back into molecular oxygen. This is correct.
$(iv)$ $CFCs$ (Chlorofluorocarbons) release chlorine atoms in the stratosphere,which react with ozone,causing an imbalance between its production and degradation. This is correct.
$(v)$ $DNA$ and proteins of living organisms absorb high-energy $UV$ rays,which can cause damage to their structure. This is correct.
Therefore,statements $(i), (iii), (iv),$ and $(v)$ are correct. Since this specific combination is not explicitly listed in the options provided,we re-evaluate the standard interpretation. Given the options,$(i), (iv),$ and $(v)$ are definitely correct,and $(iii)$ is also scientifically accurate. If we must choose the most appropriate set,$(i), (iii), (iv)$ is often grouped in textbooks.

(D) The correct answer is $D$. The statement '$UV-B$ rays cannot be absorbed by the cornea' is incorrect because the cornea of the human eye absorbs $UV-B$ radiation. High doses of $UV-B$ cause inflammation of the cornea,a condition known as snow-blindness,cataract,etc. $UV-A$ is mostly absorbed by the atmosphere,while $UV-B$ is partially absorbed by the ozone layer,but a significant amount reaches the Earth's surface.

(B) Ozone protects us from the harmful $UV$ radiations from the sun. The major pollutants responsible for the depletion of the ozone layer are chlorofluorocarbons $(CFCs)$,nitrogen oxides,and hydrocarbons.
$CFCs$ are widely used as coolants in air conditioners and refrigerators,cleaning solvents,aerosol propellants,and in foam insulation. The threat to $O_3$ is mainly from $CFCs$,which are known to deplete $O_3$ by $14\%$ at the current emission rate.

(A) $UV-A$ radiation has the longest wavelength,ranging from $320-390\, nm$,and is the least harmful form of $UV$ radiation.
Because of its longer wavelength,it is not absorbed by the ozone layer and is allowed to pass through to reach the Earth's surface.
In contrast,$UV-B$ and $UV-C$ are largely absorbed by the ozone layer,with $UV-C$ being the most harmful.

(D) Ozone depletion in the stratosphere allows more ultraviolet $(UV)$ radiation to reach the Earth's surface. Increased exposure to $UV-B$ radiation is known to cause $DNA$ damage,leading to an increased incidence of skin cancer and cataracts in humans.

(A) $O_3$ (Ozone) is a powerful oxidizing agent. It effectively kills bacteria,viruses,and other microorganisms present in the water,thereby acting as an efficient disinfectant for swimming pools.

(B) The ozone layer is located in the stratosphere,approximately $20-26 \ km$ above sea level.
Chlorofluorocarbons $(CFCs)$ release active chlorine radicals when exposed to $UV$ radiation.
These active chlorine radicals act as catalysts to destroy the ozone layer by converting ozone $(O_3)$ into oxygen $(O_2)$.
$A$ single chlorine radical can destroy up to $1000$ ozone molecules,leading to the depletion of the ozone layer.

(B) The depletion of ozone is particularly marked over the Antarctic region, which was first reported in $1985$.
This phenomenon has resulted in the formation of a large area of a thinned ozone layer, which is commonly referred to as the ozone hole.

(C) The primary cause of ozone layer depletion is the release of chlorofluorocarbons $(CFCs)$ into the atmosphere.
These compounds are released from sources such as aerosol spray cans,polyurethane foams,air conditioners,and refrigerators.
Once in the stratosphere,$CFCs$ break down under ultraviolet radiation to release chlorine atoms,which catalyze the destruction of ozone molecules.

(B) The ozone hole is not an actual physical hole in the atmosphere. It refers to an area of extreme reduction in ozone concentration within the ozone layer located in the stratosphere.

(A) $CFCs$ (Chlorofluorocarbons) are primarily responsible for ozone layer depletion.
$CFCs$ are used as refrigerants in refrigerators and air conditioners,and as propellants in aerosol sprays. When these $CFCs$ reach the stratosphere,$UV$ rays break down the $CFC$ molecules,releasing chlorine $(Cl)$ atoms (free radicals).
These chlorine free radicals react with ozone $(O_3)$ to convert it into oxygen $(O_2)$,thereby reducing the ozone content in the atmosphere. The reaction is as follows:
$Cl + O_3 \rightarrow ClO + O_2$
$ClO + O \rightarrow Cl + O_2$
One chlorine free radical is sufficient to destroy a large number of ozone molecules because the chlorine radical is regenerated in the process,allowing it to continue the cycle of ozone destruction.

(B) Ozone $(O_3)$ is an allotrope of oxygen. It exists at a height of about $15-60 \,km$ in the stratosphere.
Chlorofluorocarbons $(CFCs)$,nitrogen oxides,and certain hydrocarbons are primary pollutants responsible for ozone layer depletion.
Among the given options,methane $(CH_4)$ is a hydrocarbon that can contribute to ozone depletion through complex atmospheric reactions.
Therefore,methane is the correct answer.

(A) The Montreal Protocol was signed in $1987$ in Montreal,Canada,to control the emission of ozone-depleting substances $(ODS)$ such as chlorofluorocarbons $(CFCs)$. This international treaty was designed to protect the ozone layer by phasing out the production and consumption of these harmful substances. Therefore,the correct option is $A$.

(B) The 'Montreal Protocol' was signed in Montreal,Canada,in $1987$. The primary objective of this international treaty was to protect the ozone layer by phasing out the production and consumption of ozone-depleting substances,such as chlorofluorocarbons $(CFCs)$.

(C) The thickness of the ozone layer in a column of air from the ground to the top of the atmosphere is measured in terms of Dobson units $(DU)$.
One Dobson unit is the thickness of $0.01 \ mm$ of ozone at standard temperature and pressure $(STP)$.
Therefore,the correct option is $C$.

(N/A) Ozone found in the upper part of the atmosphere,called the stratosphere,acts as a shield by absorbing ultraviolet $(UV)$ radiation from the sun.
$UV$ rays are highly injurious to living organisms.
The thickness of the ozone layer in a column of air from the ground to the top of the atmosphere is measured in terms of Dobson units $(DU)$.
Ozone layer absorbs the harmful $UV$-rays.
$UV$ radiation causes aging of the skin,damage to skin cells,and various types of skin cancers.
In the human eye,the cornea absorbs $UV-B$ radiation,and a high dose of $UV-B$ causes inflammation of the cornea,called snow-blindness,cataract,etc.
Such exposure may permanently damage the cornea.
Chlorofluorocarbons $(CFCs)$ deplete the ozone layer.
The part of the atmosphere with a lesser concentration of ozone is called an ozone hole.
Steps leading to ozone depletion:
$1$. $UV$-rays split $CFCs$ and release atomic chlorine $(Cl)$.
$2$. $UV$-rays also split ozone into oxygen.
$3$. Chlorine atoms trap oxygen atoms,and ozone is not formed again from oxygen.
This leads to the depletion of ozone in the stratosphere.

(B) Recognizing the deleterious effects of ozone depletion,an international treaty,known as the Montreal Protocol,was signed at Montreal (Canada) in $1987$ (effective in $1989$) to control the emission of ozone-depleting substances.
Subsequently,many more efforts have been made,and protocols have laid down definite roadmaps,separately for developed and developing countries,for reducing the emission of $CFCs$ and other ozone-depleting chemicals.

(B) The formation of the ozone hole over Antarctica is primarily due to extreme low temperatures $(-85^{\circ}C)$.
These temperatures lead to the formation of polar stratospheric clouds (ice clouds).
These clouds provide a catalytic surface for the reactions of chlorine atoms,which deplete the ozone layer.
Additionally,a polar vortex is formed,which isolates the air over Antarctica from the rest of the world,preventing the replenishment of ozone.

(B) The Montreal Protocol was signed in $1987$ in Montreal,Canada,to control the emission of ozone-depleting substances.
It officially became effective in $1989$.

(A) The solar spectrum consists of various wavelengths of electromagnetic radiation.
Ultraviolet $(UV)$ radiation,particularly $UV-B$ and $UV-C$,has high energy and can damage biological molecules such as $DNA$ and proteins,leading to mutations and cell death.
While visible light is essential for photosynthesis and infrared radiation provides heat,$UV$ radiation is specifically known for its harmful effects on living organisms,including skin cancer and cataracts in humans.

(D) $1$. Ozone found in the upper part of the atmosphere,specifically the $Stratosphere$,is called 'good' ozone because it acts as a shield absorbing harmful $UV$ radiation from the sun.
$2$. Ozone found in the lower part of the atmosphere,the $Troposphere$,is considered 'bad' ozone because it is a pollutant that can be harmful to plants and animals.
$3$. Therefore,good ozone is in the $Stratosphere$ and bad ozone is in the $Troposphere$.

(A) The ozone layer is present in the stratosphere of the Earth's atmosphere.
It acts as a shield by absorbing the harmful ultraviolet $(UV)$ radiation coming from the Sun.
These $UV$ rays are highly energetic and can cause damage to living organisms,such as skin cancer,cataracts,and $DNA$ mutations.
Therefore,the ozone layer prevents the entry of $UV$ rays into the lower atmosphere.