Q.What is ozone hole?
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Stratospheric ozone — "good" ozone, distinct from the harmful "bad" ozone found near ground level — forms a protective layer in the upper atmosphere that absorbs dangerous ultraviolet (UV) radiation from the Sun before it can reach the surface, since UV radiation readily damages the DNA and proteins of living organisms. The total ozone in a vertical air column is measured in Dobson units.
Ozone is continuously formed and broken down in the stratosphere, normally in a stable balance; this balance is disrupted by chlorofluorocarbons (CFCs), widely used as refrigerants, which drift up into the stratosphere where UV radiation splits them apart, releasing chlorine atoms that catalytically destroy ozone without themselves being consumed — so a single chlorine atom can degrade many ozone molecules, giving CFCs long-lasting effects on ozone levels. Depletion is most severe over Antarc …
An ozone hole is a region of the stratosphere where the protective ozone layer has thinned drastically, letting far more harmful UV radiation reach the surface. …
Step 1. Recall that the stratospheric ozone layer normally acts as a protective shield, absorbing most of the sun's ultraviolet radiation before it reaches the ground, and that its thickness is measured in Dobson Units (an average of about 300 DU globally).
Step 2. Certain man-made chemicals released at Earth's surface — chlorofluorocarbons (CFCs) used in refrigeration, aerosols and industrial cleaning being the chapter's named culprit — rise into the stratosphere and chemically break down ozone molecules.
Step 3. When this breakdown is severe and concentrated over a particular region (rather than spread evenly worldwide), the local ozone-column thickness drops sharply, and this restricted-area zone of severely depleted ozone is what is termed an 'ozone hole.' …
Recall the chapter's own definition — 'the decline in the thickness of the ozone layer over a restricted area is called Ozone hole' — and …
- Confusing 'ozone hole' with total absence of ozone rather than a severe localised thinning. …
Showing the 12 most recent of 14 on this concept.
- CBSE 2025Set F1 markMCQQ.Which of the following is most harmful to the ozone layer?(a) SO2(b) CO2(c) Freon(d) All of these
›Reveal solutionSolution
Freon (CFC) is the most harmful to the ozone layer.
Freons are chlorofluorocarbons (CFCs). In the stratosphere, UV radiation releases active chlorine (Cl) radicals from CFCs, and each Cl radical catalytically breaks down thousands of ozone (O3) molecules without being consumed, thinning the ozone layer. This is the main ca …
- CBSE 2025Set ANNUAL1 markQ.In which part of atmosphere, sufficient quantity of ozone is found?
›Reveal solutionSolution
The ozone layer lies in the stratosphere, the atmospheric layer above the troposphere.
Earth's atmosphere is divided into several layers based on temperature and composition: troposphere (closest to the surface), stratosphere, mesosphere, thermosphere, and exosphere. Within the stratosphere, at an altitude of about 16 to 26 km, ozone (O3) is present in a much higher concentration than elsewhere in the atmosphere, forming what is popularly called the 'ozone layer' or 'ozonosphere'. This ozone is continuously formed by the action of UV radiation on molecular oxygen and, in turn, absorbs most of the harmful UV-B radiation from the sun, shielding life on Earth from its damaging effe …
- CBSE 2025Set ANNUAL1 markMCQQ.The 'thickness' of Stratospheric Ozone layer is measured in :(a) Melson units(b) Sieverts units(c) Beaufort scale(d) Dobson units
›Reveal solutionSolution
Stratospheric ozone-layer thickness is measured in Dobson units, a standard unit for total column ozone.
The stratospheric ozone layer, which absorbs most of the sun's harmful ultraviolet-B radiation, varies in thickness across the globe and over time; scientists monitor this using the Dobson unit (DU), a measure of the total amount of ozone in a vertical column of atmosphere. One Dobson unit is defined as the thickness (in units of 0.01 mm) that the total ozone in that column would occupy if compressed to a layer of pure gas at standard temperature and pressure -- a typical global average is around 300 DU, and a significant depletion below this (as observed over Antarctica, the 'ozone hole') indicates …
- CBSE 2024Set ANNUAL1 markMCQQ.Ozone layer in upper atmosphere is destroyed by :(a) CFCs(b) SO2(c) O2 and CO2(d) Smog.
›Reveal solutionSolution
Chlorofluorocarbons (CFCs), used in refrigerants and aerosol propellants, catalytically break down stratospheric ozone (O3) into O2, thinning the protective ozone layer.
The stratospheric ozone layer absorbs harmful UV-B radiation from the sun, protecting life on Earth. Chlorofluorocarbons (CFCs) — synthetic compounds once widely used in refrigerators, air conditioners and aerosol sprays — are highly stable and rise into the stratosphere, where UV radiation breaks them down and releases chlorine atoms. Each chlorine atom acts as a catalyst, breaking apart thousands of ozone molecules without itself being consumed, leading to ozone depletion (the 'ozone hole', dramatically seen over Antarctica). SO2 and smog are more associated with ground-level (tropospheric) air pollution and acid rain, …
- CBSE 2024Set ANNUAL1 markMCQQ.The International Ozone day is :(a) June 05(b) March 21(c) September 16(d) May 22
›Reveal solutionSolution
International Ozone Day is observed on September 16, marking the anniversary of the 1987 Montreal Protocol.
Working
The International Day for the Preservation of the Ozone Layer (commonly called World/International Ozone Day) is observed on September 16 each year. The date commemorates the signing of the Montreal Protocol on Substances that Deplete the Ozone Layer on 16 September 1987, a landmark international agreement to phase out the production of ozone-depleting substances such as chlorofluorocarbons (CFCs). The other dates listed are …
- CBSE 2023Set ANNUAL1 markQ.What is the full form of C.F.C. gas?
›Reveal solutionSolution
C.F.C. stands for Chlorofluorocarbon, a gas implicated in ozone-layer depletion.
CFC stands for Chlorofluorocarbon — synthetic compounds containing carbon, chlorine and fluorine, once widely used as refrigerants, propellants in aerosol sprays, and solvents. When released into the atmosphere, CFCs rise to the stratosphere where UV radiation breaks them down, releasing chlorine free radicals that catalytically destroy stratospheric ozone …
- CBSE 2023Set ANNUAL1 markMCQQ.Depletion of __________ gas in the atmosphere can lead to an increased incidence of skin cancer.(a) Nitrous oxide(b) Ammonia(c) Ozone(d) Methane
›Reveal solutionSolution
Depletion of the stratospheric ozone layer lets more harmful UV-B radiation reach the Earth's surface, increasing the incidence of skin cancer.
Working
The ozone layer in the stratosphere absorbs the great majority of the sun's harmful ultraviolet-B (UV-B) radiation before it reaches the ground. Ozone depletion, caused mainly by anthropogenic chlorofluorocarbons (CFCs), halons and related ozone-depleting substances, thins this protective layer -- most dramatically seen as the "ozone hole" over Antarctica.
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- CBSE 2022Set ANNUAL1 markQ.Whose thickness in the atmosphere is measured by Dobson Unit (DU)?
›Reveal solutionSolution
The Dobson Unit is the standard unit for measuring the total amount (thickness) of ozone in the atmosphere's ozone layer.
Dobson Unit (DU):
The Dobson Unit is named after G.M.B. Dobson, one of the first scientists to study atmospheric ozone. It expresses the total amount of ozone in a vertical column of the atmosphere above a given location, if that ozone were compressed into a single layer at standard temperature and pressure.
1 DU corresponds to a layer of ozone 0.01 mm thick under standard conditions. Normal atmospheric ozone-layer thickness is around 300 DU.
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- CBSE 2021Set ANNUAL1 markQ.Write full name of CFCs.
›Reveal solutionSolution
CFCs (Chlorofluorocarbons) are synthetic organic compounds once widely used as refrigerants and aerosol propellants; they are notorious for depleting the stratospheric ozone layer.
CFCs are compounds made of carbon, chlorine, and fluorine atoms (e.g., CFC-11, CFC-12; commercially known as Freons). They were widely used in refrigerators, air conditioners, aerosol sprays, and foam-blowing agents because they are stable, non-toxic, and non-flammable at ground level.
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- CBSE 2020Set ANNUAL1 markMCQQ.Which of the following is the cause of skin cancer and high mutation rate?(a) CO2 pollution(b) CO pollution(c) Acid rain(d) Ozone depletion
›Reveal solutionSolution
Depletion of the stratospheric ozone layer lets more ultraviolet-B (UV-B) radiation reach the Earth's surface, and this UV-B is what causes skin cancer and increased mutation rates.
The ozone (O3) layer in the stratosphere absorbs most of the Sun's harmful ultraviolet radiation, particularly UV-B, protecting living organisms on Earth's surface. Human-released chemicals — chiefly chlorofluorocarbons (CFCs), used in refrigerants, aerosols, and foam-blowing agents — rise into the stratosphere and catalytically break down ozone molecules, thinning the ozone layer (most dramatically over Antarctica, the 'ozone hole').
As the ozone layer thins, more UV-B radiation penetrates to the Earth's surface. UV-B is a high-energy, mutagenic form of radiation that:
- Damages DNA directly (forms pyrimidine dimers), increasing the mutation rate in exposed cells. …
- CBSE 2020Set ANNUAL1 markMCQQ.The thickness of the ozone in a column of air is measured in(a) Decibel(b) Dobson unit(c) Barometer(d) Thermometer
›Reveal solutionSolution
The Dobson unit is the standard measure of atmospheric ozone-column thickness, widely used to track ozone-layer depletion.
The thickness of the ozone layer — more precisely, the total amount of ozone present in a vertical column of air extending from the Earth's surface to the top of the atmosphere — is measured in Dobson units (DU), named after G.M.B. Dobson, a pioneer of atmospheric ozone research. One Dobson unit is defined as the amount of ozone that, if brought to standard temperature and pressure (0°C, 1 atmosphere), would form a layer 0.01 mm thick. A typical, healthy total-column ozone measurement is around 300 DU; measurements at the Antarctic "ozone hole" during its most depleted periods have historically fallen to around 100 DU or lower, illustrating the …
- CBSE 2019Set ANNUAL1 markMCQQ.Ozone depletion is caused by(a) [illegible in source - a single garbled glyph, likely a font/subscript rendering corruption](b) CFC(c) heat(d) DDT
›Reveal solutionSolution
Ozone depletion is chiefly caused by chlorofluorocarbons (CFCs) released into the atmosphere.
The stratospheric ozone layer absorbs most of the sun's harmful ultraviolet (UV-B) radiation before it reaches the Earth's surface. Chlorofluorocarbons (CFCs) — synthetic compounds once widely used as refrigerants, aerosol propellants and solvents — are stable enough to rise unreacted into the stratosphere, where intense UV radiation breaks them apart, releasing highly reactive chlorine atoms. Each chlorine atom can catalytically destroy thousands of ozone (O3) molecules, converting them back to O2 and thinning the ozone layer (famously creating the 'ozone hole' over Antarctica). This lets more harmful UV-B radiation reach the surface, increasing risks such as skin cancer and cataracts, and harming plant/aquatic life.
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