Ozone Depletion in the Stratosphere Questions in English

(C) Ultraviolet $(UV)$ radiations from the sun act on molecular oxygen $(O_2)$ in the upper atmosphere (stratosphere).
These radiations split the $O_2$ molecules into free oxygen atoms $(O + O)$.
These free oxygen atoms then combine with molecular oxygen $(O_2)$ to form ozone $(O_3)$ through the reaction: $O_2 + O \rightarrow O_3$.

(B) The Earth's atmosphere contains a layer of $O_3$ (Ozone) in the stratosphere.
This layer acts as a protective shield by absorbing the majority of the harmful ultraviolet $(UV)$ radiation emitted by the Sun.
Without this layer, these radiations would reach the Earth's surface, causing severe damage to living organisms, including $DNA$ mutations and skin cancer.
Therefore, the correct answer is $Ozone$.

(D) Ultraviolet $(UV)$ radiations are a form of non-ionizing radiation that can damage the $DNA$ in skin cells.
Chronic exposure to these radiations leads to mutations in the genetic material,which can cause the cells to divide uncontrollably,resulting in skin cancer.
Therefore,skin cancer is the most direct consequence of prolonged exposure to harmful $UV$ rays.

(B) The depletion of the ozone layer,commonly referred to as the 'ozone hole',is most prominently observed over the $Antarctica$ region,which is located at the $South$ $pole$.
This phenomenon occurs due to the accumulation of chlorofluorocarbons $(CFCs)$ and the unique atmospheric conditions,such as polar stratospheric clouds,that facilitate the chemical reactions destroying ozone molecules.

(A) The 'Earth Summit' held in $1992$ in Rio de Janeiro,Brazil,focused on global environmental conservation. $A$ significant outcome was the international agreement to phase out the use of chlorofluorocarbons $(CFCs)$ by the end of the year $2000$. $CFCs$ are potent ozone-depleting substances that cause the thinning of the ozone layer in the stratosphere.

(C) Ultraviolet $(UV)$ radiation from sunlight plays a crucial role in the formation of ozone $(O_3)$ in the stratosphere.
When high-energy $UV$ radiation strikes oxygen molecules $(O_2)$,it causes them to split into two individual oxygen atoms $(O + O)$.
These highly reactive oxygen atoms then collide with other oxygen molecules $(O_2)$ to form ozone $(O_3)$ molecules $(O + O_2 \rightarrow O_3)$.
This process is essential for creating the ozone layer,which protects the Earth from harmful $UV$ radiation.

(C) The term 'ozone hole' does not refer to an actual physical hole in the atmosphere.
Instead,it refers to a significant thinning or decrease in the concentration of ozone $(O_3)$ in the stratosphere,particularly over the Antarctic region.
This depletion is primarily caused by the release of chlorofluorocarbons $(CFCs)$ and other ozone-depleting substances.

(B) The stratosphere layer of the Earth's atmosphere contains a concentration of ozone $(O_3)$ gas. This ozone layer acts as a shield by absorbing high-energy ultraviolet $(UV)$ radiation from the sun,preventing approximately $99\%$ of these harmful rays from reaching the Earth's surface. Thus,it protects the biosphere from the damaging effects of $UV$ radiation.

(C) The concentration of ozone in the atmosphere is measured in Dobson Units $(DU)$.
One Dobson Unit is defined as $0.01 \ mm$ thickness of ozone at standard temperature and pressure $(STP)$.
In terms of concentration,the ozone layer in the stratosphere has a concentration of approximately $10 \ ppm$ (parts per million),which is considered the maximum concentration compared to other atmospheric layers.

(D) Chlorofluorocarbons (CFCs),commonly known as freons,are stable compounds that reach the stratosphere. In the presence of ultraviolet radiation,they release chlorine atoms,which catalytically destroy ozone $(O_3)$ molecules,leading to the depletion of the ozone layer. Similarly,nitrogen dioxide $(NO_2)$ also contributes to the depletion of the ozone layer through complex chemical reactions in the stratosphere.

(C) The correct answer is $(C)$.
Chlorofluorocarbons $(CFCs)$ are stable, non-toxic, and non-flammable chemicals that were widely used in refrigerators, air conditioners, and aerosol sprays.
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 $(O_3)$ molecules into oxygen $(O_2)$, leading to the depletion of the ozone layer.

(B) The ozone layer in the stratosphere is primarily depleted by chemicals that release chlorine or bromine atoms upon exposure to ultraviolet radiation.
Chlorofluorocarbons $(CFCs)$ are the most significant contributors to ozone depletion.
Nitrogen oxides $(NO_x)$ also play a role in the catalytic destruction of ozone.
Therefore,nitrogen oxides and fluorocarbons (specifically $CFCs$) are the chief pollutants responsible for this phenomenon.

(B) The depletion of the ozone layer,commonly referred to as the ozone hole,is most pronounced over the continent of $Antarctica$.
This phenomenon occurs primarily due to the unique atmospheric conditions in the polar region,specifically the formation of polar stratospheric clouds during the extremely cold winter months.
These clouds provide a surface for chemical reactions that release active chlorine from chlorofluorocarbons $(CFCs)$,which then catalyze the destruction of ozone molecules $(O_3)$.

(B) The stratospheric ozone layer acts as a shield that absorbs harmful ultraviolet $(UV)$ radiation from the sun.
Depletion of this layer allows more $UV-B$ radiation to reach the Earth's surface.
$UV-B$ radiation damages $DNA$ and induces mutations,which significantly increases the incidence of skin cancers and cataracts in humans.
While global warming is primarily caused by greenhouse gases and forest fires are often related to climate change or human activity,the direct and most scientifically established consequence of ozone depletion is the increased exposure to harmful $UV$ radiation leading to skin cancers.

(D) The correct answer is $D$.
As the ozone layer in the stratosphere becomes thinner or develops holes,it allows a higher intensity of harmful ultraviolet $(UV)$ radiations to reach the Earth's surface.
These $UV$ radiations,particularly $UV-B$,are known to cause $DNA$ damage in skin cells,which can lead to skin-related disorders such as skin cancer (e.g.,melanoma) and premature aging of the skin.

(B) The ozone layer is present in the stratosphere region of the atmosphere.
This layer acts as a shield by absorbing harmful ultraviolet $(UV)$ radiation from the sun.
An 'ozone hole' refers to the depletion of this protective layer,which allows a higher intensity of harmful $UV$ radiation to reach the Earth's surface.
Therefore,the direct result of the ozone hole is the increased penetration of $UV$ radiation.

(B) $CFCs$ (Chlorofluorocarbons) are chemical compounds that,when released into the atmosphere,reach the stratosphere.
In the stratosphere,they are broken down by ultraviolet radiation,releasing chlorine atoms.
These chlorine atoms react with ozone $(O_3)$ molecules,leading to the destruction of the ozone layer.
Because this depletion allows harmful ultraviolet radiation to reach the Earth's surface,the use of $CFCs$ in refrigerators and air conditioners is restricted and not recommended.

(B) Chlorofluorocarbons (CFCs) are the primary substances responsible for the depletion of the ozone layer.
These compounds 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 $(O_3)$ molecules into oxygen $(O_2)$,thereby thinning the ozone layer.

(A) The stratosphere contains a layer of $O_3$ (Ozone) gas.
This ozone layer acts as a shield by absorbing the harmful ultraviolet $(UV)$ radiations coming from the sun.
These $UV$ radiations can cause skin cancer,cataracts,and damage to $DNA$ in living organisms.
Therefore,the correct answer is Ozone.

(B) 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.
By preventing these high-energy $UV$ rays from reaching the Earth's surface,it protects living organisms from harmful effects such as skin cancer,cataracts,and $DNA$ damage.
Therefore,the presence of ozone is crucial for life on Earth as it checks the penetration of ultraviolet rays.

(C) 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 numerous substances that are responsible for ozone depletion.
Therefore,the correct option is $C$.

(D) The atmosphere is divided into several layers based on temperature and altitude.
Ozone $(O_3)$ is present in different layers of the atmosphere.
In the stratosphere (the layer above the troposphere), ozone is formed by the action of $UV$ rays on molecular oxygen. This is known as "good ozone" because it acts as a shield, absorbing harmful $UV$ radiation from the sun and protecting life on Earth.
Conversely, ozone found in the troposphere is considered "bad ozone" as it is a pollutant that can be harmful to plants and animals.
Therefore, the correct answer is stratosphere.

(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 by this protocol are chlorofluorocarbons $(CFCs)$ and other ozone-depleting chemicals.
Therefore,the correct option is $B$.

(D) The Montreal Protocol is an international treaty designed to protect the ozone layer by phasing out the production of numerous substances that are responsible for ozone depletion.
It was originally signed on September $16, 1987$,and came into force on January $1, 1989$.
Therefore,the correct year in which it was passed is $1987$.

(B) Jet planes fly in the stratosphere,where they release various gases.
Among the pollutants emitted by jet engines,$CFC$s (Chlorofluorocarbons) are significant because they contribute to the depletion of the ozone layer.
While other gases like $SO_2$,$CO$,and $NO_x$ are also emitted,$CFC$s are specifically noted in environmental studies regarding stratospheric pollution caused by high-altitude aircraft.

(B) The stratosphere contains a layer of ozone $(O_3)$ gas. This ozone layer acts as a shield by absorbing the harmful ultraviolet $(UV)$ radiation coming from the sun. This prevents the $UV$ rays from reaching the Earth's surface,thereby protecting living organisms from potential damage such as skin cancer and cataracts.

(C) The ozone layer in the stratosphere is primarily depleted by $Chlorofluorocarbons$ $(CFCs)$.
$CFCs$ are released into the atmosphere from refrigerators,air conditioners,and aerosol sprays.
In the stratosphere,these compounds are broken down by ultraviolet $(UV)$ radiation,releasing chlorine atoms.
These chlorine atoms act as catalysts to break down ozone $(O_3)$ molecules into oxygen $(O_2)$,leading to the thinning of the ozone layer.

(D) The correct answer is $D$.
Ozone $(O_3)$ layer is present in the stratosphere and acts as a protective shield against harmful $UV$ radiations coming from the sun.
$UV$ radiations are highly energetic and can cause mutations in the $DNA$ of living organisms.
Depletion or thinning of the ozone layer allows a higher intensity of $UV$ radiations to reach the Earth's surface.
Increased exposure to these radiations leads to various health issues,including an increased incidence of skin cancers,cataracts,impaired vision,sunburns,and a weakened immune system.

(B) $UV$ radiations are of three types: $UV-C$ $(100-280 \ nm)$,$UV-B$ $(280-320 \ nm)$,and $UV-A$ $(320-390 \ nm)$.
Shorter $UV$ radiations $(UV-C)$ are absorbed by the atmosphere.
The longer ones $(UV-A)$ are not very harmful.
The intermediate $UV-B$ radiations are harmful and capable of deep penetration.
Thinning of the ozone layer increases the amount of $UV-B$ radiations reaching the Earth.
$UV-B$ radiations damage skin cells,cause skin ageing,skin cancer,and eye damage (such as snow blindness or cataracts),and can also suppress the immune system.
Liver cancer is not directly associated with $UV$ radiation exposure.

(C) The correct answer is $C$. The ozone layer or ozone shield is present in the stratosphere.
It functions as a protective shield against strong $UV$ radiations coming from the sun.
$UV$ radiations are highly harmful and can cause mutations in living organisms.
Thinning of the ozone layer increases the amount of $UV$ radiations reaching the Earth.
This leads to an increased occurrence of cataracts,skin cancers,vision impairment,photoburning,and a weakened immune system.

(C) : "Bad ozone" is formed in the lower atmosphere (troposphere) that harms plants and animals.
"Good ozone" is found in the upper part of the atmosphere called the stratosphere and it acts as a shield, absorbing ultraviolet $(UV)$ radiation from the sun.
$UV$ rays are highly injurious to living organisms because the $DNA$ and proteins of living organisms preferentially absorb $UV$ rays, and their high energy breaks the chemical bonds within these molecules.

(A) The correct answer is $A$. The Montreal Protocol was signed in Montreal,Canada,by over $150$ countries at a convention in $1987$ to reduce the use of $CFCs$ (chlorofluorocarbons).
The primary aim of this protocol was to protect the ozone layer in the stratosphere by decreasing and eventually eliminating the use of ozone-depleting substances,such as $CFCs$.
It is widely regarded as one of the most successful international environmental treaties in modern history.

(D) The correct answer is $D$. The Montreal Protocol was signed in Montreal,Canada,by over $150$ countries at a convention in $1987$ to control the use of $CFCs$ (chlorofluorocarbons).
The primary objective of this protocol was to protect the ozone layer in the stratosphere by decreasing and eventually eliminating the use of ozone-depleting substances,such as $CFCs$.
It is widely regarded as one of the most successful international environmental treaties in modern history.

(C) The correct answer is $C$.
The Montreal Protocol was signed in Montreal,Canada,by over $150$ countries at a convention in $1987$ to reduce the use of $CFCs$ (chlorofluorocarbons).
The primary aim of this protocol was to protect the ozone layer in the stratosphere by decreasing and eventually eliminating the use of ozone-depleting substances,such as $CFCs$.
It is widely regarded as one of the most successful international environmental treaties in modern history.

(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 goal is to reduce the emission of ozone-depleting substances like chlorofluorocarbons $(CFCs)$.

(D) $UV-B$ radiation is highly energetic and can cause significant biological damage.
$1$. It is absorbed by $DNA$ and proteins,causing mutations that lead to various types of skin cancer.
$2$. It is absorbed by the cornea of the human eye,causing inflammation of the cornea,a condition known as snow-blindness.
$3$. It also causes permanent damage to the cornea.
$4$. Barrier in blood transport is not a known effect of $UV-B$ radiation exposure.

(A) In the stratosphere,chlorofluorocarbons ($CFC$s) are broken down by ultraviolet $(UV)$ radiation.
This process releases chlorine atoms $(Cl)$ into the atmosphere.
These chlorine atoms act as catalysts in the degradation of ozone $(O_3)$ into oxygen $(O_2)$,leading to the depletion of the ozone layer.

(C) The depletion of the ozone layer is primarily caused by chlorofluorocarbons $(CFCs)$.
$CFCs$ are released into the atmosphere from refrigerators,air conditioners,and aerosol sprays.
Once they reach the stratosphere,they are broken down by ultraviolet $(UV)$ radiation,releasing chlorine atoms.
These chlorine atoms act as catalysts in the destruction of ozone $(O_3)$ molecules,converting them into oxygen $(O_2)$.

(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 chemical reaction that converts ozone $(O_3)$ into oxygen $(O_2)$.
One chlorine atom can destroy thousands of ozone molecules because it is not consumed in the reaction,thus acting as a catalyst.

(B) $1$. $CFCs$ (Chlorofluorocarbons) react with ozone in the stratosphere,leading to the depletion (thinning) of the ozone layer,not thickening. Thus,option $A$ is incorrect.
$2$. $UV-B$ radiation is highly damaging to living organisms. Prolonged exposure to $UV-B$ causes inflammation of the cornea,known as snow blindness,and can also lead to cataracts. Thus,option $B$ is correct.
$3$. 'Good' ozone is found in the stratosphere,which protects us from harmful $UV$ radiation. Ozone in the troposphere is considered a pollutant ('bad' ozone). Thus,option $C$ is incorrect.
$4$. The Montreal Protocol was signed in $1987$ to control the emission of ozone-depleting substances,specifically $CFCs$,to protect the ozone layer. It is not primarily concerned with the greenhouse effect (which is addressed by the Kyoto Protocol). Thus,option $D$ is incorrect.

(B) The ozone layer is present in the stratosphere of the Earth's atmosphere.
It acts as a shield by absorbing harmful ultraviolet $(UV)$ radiation coming from the Sun.
This prevents $UV$ rays from reaching the Earth's surface,thereby protecting living organisms from harmful effects like skin cancer,cataracts,and $DNA$ damage.

(D) The incorrect statement is $D$. In the human eye,the cornea absorbs $UV-B$ radiation,not the choroid. $A$ high dose of $UV-B$ causes inflammation of the cornea,a condition known as snow-blindness. The other statements are correct: $UV$ rays are harmful because they are absorbed by $DNA$ and proteins,causing chemical bond breakage. In the stratosphere,$UV$ rays break down $CFCs$ to release $Cl$ atoms,which deplete the ozone layer. $UV-B$ is known to cause $DNA$ damage and mutations.

(D) Jet planes release gaseous emissions at high altitudes. The major aerosol pollutant released by jet planes is $CFCs$ (Chlorofluorocarbons). These $CFCs$ are released in the stratosphere,where they break down to release chlorine atoms,which subsequently deplete the ozone layer.

(A) In the stratosphere, ultraviolet $(UV)$ radiation acts on molecular oxygen $(O_2)$ to split it into free oxygen atoms $(O)$.
These free oxygen atoms then react with molecular oxygen $(O_2)$ to form ozone $(O_3)$.
The chemical reaction is as follows:
$O_2 + \text{UV} \rightarrow O + O$
$O + O_2 \rightarrow O_3$
Therefore, the correct product is ozone $(O_3)$.

(B) The ozone hole is a region of exceptionally depleted ozone in the stratosphere over the Antarctic.
It is most prominent over Antarctica because the extremely cold temperatures during the polar winter lead to the formation of polar stratospheric clouds.
These clouds provide surfaces for chemical reactions that convert inactive chlorine into active forms,which then destroy ozone molecules when sunlight returns in the spring.

(D) The depletion of the ozone layer allows more ultraviolet $(UV)$ radiation,specifically $UV-B$,to reach the Earth's surface.
Increased exposure to $UV-B$ radiation is known to cause various skin-related issues,including premature aging of the skin,skin cancer,and damage to $DNA$ in skin cells.
Therefore,as the ozone layer continues to deplete,the incidence of skin-related diseases is expected to rise.

(D) Supersonic jets emit nitrogen oxides $(NO_x)$ into the stratosphere.
These nitrogen oxides react with ozone $(O_3)$ and cause its depletion or thinning.
Therefore,supersonic jets contribute to the thinning of the ozone layer ($O_3$ layer).

(A) The Montreal Protocol is an international treaty designed to protect the ozone layer by phasing out the production of numerous substances that are responsible for ozone depletion.
It was agreed upon on $16$ September $1987$ in Montreal,Canada,and came into force on $1$ January $1989$.
Therefore,the correct year is $1987$.

(A) The $Montreal$ $Protocol$ is an international treaty designed to protect the ozone layer by phasing out the production of numerous substances that are responsible for ozone depletion. It was signed in $1987$ and came into force in $1989$.
$Kyoto$ $Protocol$ is related to the reduction of greenhouse gases to combat global warming.
$Vienna$ $Convention$ provided the framework for international cooperation on ozone protection but the specific measures for reduction were detailed in the $Montreal$ $Protocol$.

(D) 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 goal is to reduce the emission of ozone-depleting substances $(ODS)$ like chlorofluorocarbons $(CFCs)$.