Question

Dobson units are used to measure thickness of [NEET 2021]

(a) CFCs

(b) stratosphere

(c) ozone

(d) troposphere

Answer/Explanation

Ans. (c)

Ozone found in stratosphere is known as good ozone or ozone layer. It acts as a shield absorbing ultraviolet radiation from the sun. The thickness of ozone in a column of air from the ground to the top of the atmosphere is measured in terms of Dobson units.

Question

 Montreal protocol was signed in 1987 for control of [NEET (Sep.) 2020]

(a) emission of ozone depleting substances

(b) release of green house gases

(c) disposal of e-wastes

(d) transport of genetically modified organisms from one country to another

Ans. (a)
Montreal protocol was signed in 1987 for control emission of ozone depleting substances. It is a global agreement to protect the stratospheric ozone layer by phasing out the production and consumption of ozone-depleting substances(ODS).

Answer/Explanation

 

Question

Which of the following statements about ozone is correct? [NEET (Odisha) 2019]

(a) Tropospheric ozone protects us from UV-radiations

(b) Stratospheric ozone is bad’

(c) Tropospheric ozone is ‘good’

(d) Stratospheric ozone protects us from UV-radiations

Answer/Explanation

Ans. (d)

Statement (d) is correct. Stratospheric ozone protects us from UV radiations of the sun. Correct information about incorrect statements is as follows. Good ozone is found in the upper part of the atmosphere, i.e. stratosphere. Bad ozone is formed in the lower atmosphere (troposphere) that harms plants and animals.

Question

World Ozone Day is celebrated on [NEET 2018]

(a) 16th September

(b) 21st April

(c) 5th June

(d) 22nd April

Answer/Explanation

Ans. (a)

World Ozone Day is celebrated on 16th September to control $\mathrm{O}_3$ depletion. Ozone layer is a fragile shield of gas that protects earth from harmful UV-rays. On 21st April the Civil Service Day and National Yellow Bat Day is celebrated. 5 th June of every year is celebrated as World Environment Day. Earth Day is an annual event, celebrated on 22nd April of every year.

Question

 In stratosphere, which one of the following elements acts as a catalyst in degradation of ozone and release of molecular oxygen? [NEET 2018]

(a) $\mathrm{Fe}$

(b) $\mathrm{Cl}$

(c) Carbon

(d) Dxygen

Answer/Explanation

Ans. (b)

In stratosphere, $\mathrm{Cl}$ acts as a catalyst in the degradation of ozone and release of molecular oxygen. It is released by action of UV rays on chlorofluorocarbon. Chlorine reacts with ozone in a series of chain reaction, converting it into oxygen. One active chlorine can destroy 5000 molecules of ozone in one month.
$
\begin{aligned}
& \mathrm{CFCl}_3 \stackrel{\mathrm{Nec}}{\longrightarrow} \mathrm{CFCl}_2+\mathrm{Cl} \\
& \mathrm{CFCl}_2 \stackrel{\mathrm{uve}}{\longrightarrow} \mathrm{CFCl}+\mathrm{Cl} \\
& \mathrm{Cl}+\mathrm{O}_3 \longrightarrow \mathrm{ClO}+\mathrm{O}_2 \\
& \mathrm{ClO}+\mathrm{O}_3 \longrightarrow \mathrm{Cl}+2 \mathrm{O}_2
\end{aligned}
$
Iron (Fe), carbon (C) and oxygen (0) are not Ozone Depleting Substances (ODS).

Question

 Depletion of which gas in the atmosphere can lead to an increased incidence of skin cancers [NEET 2016, Phase I]

(a) ozone

(b) ammonia

(c) methane

(d) nitrous oxide

Answer/Explanation

Ans. (a)

Ozone is found in the upper part of the atmosphere called stratosphere and it acts as a shield absorbing ultraviolet radiation from sun. So its depletion can lead to incidence of skin cancers caused by harmful solar radiations which will reach earth in the absence of $\mathrm{O}_3$ layer.

Question

The zone of atmosphere in which the ozone layer is present is called [CBSE AIPMT 2014]

(a) ionosphere

(b) mesosphere

(c) stratosphere

(d) troposphere

Answer/Explanation

Ans. (c)

The ozone layer is mainly found in the lower portion of stratosphere, i.e. approximately $20-30 \mathrm{~km}$ above the earth, though its thickness varies seasonally and geographically, ozone layer acts as a shield absorbing UV rays from the sun.

Question

 Which one of the following is a wrong statement? [CBSE AIPMT 2012]

(a) Most of the forests have been lost in tropical areas

(b) Ozone in upper part of atmosphere is harmful to animals

(c) Greenhouse effect is a natural phenomenon

(d) Eutrophication is a natural phenomenon in freshwater bodies

Answer/Explanation

Ans. (b)

Ozone $\left(0_3\right)$ is an isotope of oxygen which exists in so called ozone layer at a height of about $15-60 \mathrm{~km}$ in the middle and upper stratosphere and lower mesosphere. This ozone layer absorbs UV-rays of longer wavelength and protects life on Earth from damaging effects of these radiations. Ozone in the lower atmosphere (troposphere) is regarded as a pollutant.

Question

 Montreal protocol aims at [CBSE AIPMT 2009]

(a) reduction of ozone depleting substances

(b) biodiversity conservation

(c) control of water pollution

(d) control of $\mathrm{CO}_2$ emission

Answer/Explanation

Ans. (a)

In August 1989, 44 countries and EEC ratified the Montreal Protocol, which provides a mechanism to review the efficiency of control measures. They also agreed to phase out the halogens and to control and reduce other Ozone Depleting Substances (ODSs). In a policy statement called Helsinki Declaration, the attending nations agreed to phase out the production and consumption of controlled CFCs as soon as possible but not later than the year 2007 .

Question

 Global agreement in specific control strategies to reduce the release of ozone depleting substances, was adopted by [CBSE AIPMT 2009]

(a) Rio de Janerio Conference

(b) Montreal Protocol

(c) Kyoto Protocol

(d) Vienna Convention

Answer/Explanation

Ans. (b)

The Montreal Protocol is a landmark international agreement designed to protect the stratospheric ozone layer. by reducing the release of ozone depleting substances. The treaty was originally signed in 1987 and substantially amended in 1990 and 1992 . The Montreal protocol stipulates that the production and consumption of compounds that deplete ozone in the stratospherechlorofluorocarbons(CFCs), halogens, carbon tetrachloride and methyl chloroform-are to be phased out by 2000 (2005 for methyl chloroform).

Question

 Montreal protocol, which calls for appropriate action to protect the ozone layer from human activities was passed in the year [CBSE AIPMT 2006]

(a) 1986

(b) 1987

(c) 1988

(d) 1985

Answer/Explanation

Ans. (b)

In 1987, twenty seven industrialised countries signed the Montreal protocol for reduction in production and release of CFCs chlorofluorocarbons depleting ozone layer, into the atmosphere. It was followed by increasingly stringent amendments in London in 1990 and in Copenhagen in 1992.

Question

 Identify the correctly matched pair. [CBSE AIPMT 2004]

(a) Montreal protocol – Global warming

(b) Kyoto protocol – Climate change

(c) Ramsar convention – Ground water pollution

(d) Basal convention – Biodiversity conservation

Answer/Explanation

Ans. (b)

Kyoto protocol deals with climate changes while Montreal protocol deals with ozone depletion.

Question

 In coming years, skin related disorders will be more common due to [CBSE AIPMT 1997]

(a) air pollution

(b) use of detergents

(c) water pollution

(d) depletion of ozone layer

Answer/Explanation

Ans. (d)

Ozone layer is found in the stratosphere of atmosphere. It absorbs harmful ultraviolet rays coming from the sun. In coming years, when the ozone layer may become thinner, ultra-violet radiations may reach earth directly to cause cancer, especially skin cancer.

Question

 Formation of ozone hole is maximum over [CBSE AIPMT 1997]

(a) India

(b) Antarctica

(c) Europe

(d) Africa

Answer/Explanation

Ans. (b)

An ozone hole (thinning) has been formed over Antarctica as a result of damage to ozone. Most ozone is formed in the stratosphere over the equator and spread by winds around the globe.
Icy particles in polar stratospheric clouds catalyse the release of chlorine (from CFC) which destroys ozone. The thinning in ozone is maximum because in winter there is exceptionally cold.

Question

Ultraviolet radiations from sunlight cause a reaction which produces [CBSE AIPMT 1993]

(a) $\mathrm{O}_3$

(b) $ \mathrm{SO}_2 $

(c) $ \mathrm{CO}$

(d) $\mathrm{CH}_4$

Answer/Explanation

Ans. (a)

Ozone is produced by action of ultraviolet and other high energy radiations on oxygen resulting in splitting and interaction of oxygen molecules $3 \mathrm{O}_2 \rightarrow 2 \mathrm{O}_3$.
This ozone forms a layer that is also called protective umbrella at $23 \mathrm{~km}$ from earth surface.

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