Set 2 | Important Ozone Layer MCQs

Correct Answer is C.

• Ozone depletion happens when chlorofluorocarbons (CFCs) are released into the atmosphere.
• These gases trigger a series of chemical reactions that break down ozone molecules, diminishing the ozone layer’s ability to absorb ultraviolet radiation.

Correct Answer is B.

• The ozone layer in the atmosphere acts as a shield, blocking harmful ultraviolet rays from reaching the Earth’s surface, thereby protecting life on Earth.
• Gases contributing to ozone layer depletion include chlorofluorocarbons (CFCs), Halon-1211, Halon-1301, nitrous oxide, trichloroethylene, and others.

Correct Answer is B.

• The greenhouse gases contributing to ozone depletion in the troposphere include water vapor, carbon dioxide, methane, ozone, nitrous oxide, and chlorofluorocarbons (CFCs).

Correct Answer is C.

• The ozone hole is not literally a “hole” with no ozone but rather a region in the stratosphere over Antarctica where ozone levels are significantly depleted.
• This phenomenon primarily occurs during the Antarctic spring (September to November) due to the release of ozone-depleting substances (ODS), such as chlorofluorocarbons (CFCs) and halons.
• These substances undergo photochemical reactions in the presence of sunlight, releasing chlorine and bromine atoms that destroy ozone molecules.
• The extremely low temperatures in the polar stratosphere form polar stratospheric clouds (PSCs), which play a key role in these chemical reactions.
• The thinning of the ozone layer allows higher levels of harmful ultraviolet (UV-B) radiation to reach the Earth’s surface, posing risks to human health, such as skin cancer and cataracts, as well as to ecosystems.

Correct Answer is C.

• The Montreal Protocol on Substances that Deplete the Ozone Layer, a landmark international treaty under the Vienna Convention for the Protection of the Ozone Layer, aims to safeguard the ozone layer by systematically phasing out the production and consumption of ozone-depleting substances (ODS).
• Adopted in 1987 and enforced from January 1, 1989, it has become one of the most successful environmental agreements, with universal ratification by all UN member states.
• The protocol has significantly reduced the use of harmful chemicals like chlorofluorocarbons (CFCs) and halons, contributing to the gradual recovery of the ozone layer while also mitigating climate change due to the greenhouse gas properties of many ODS.
• Regular amendments and updates ensure it adapts to scientific advancements and emerging challenges.

Correct Answer is B.

• The ozone layer in the stratosphere is naturally regulated by nitrogen dioxide (NO₂), which plays a role in maintaining its balance.
• The thickness of the ozone layer fluctuates seasonally, being at its maximum during spring and at its minimum during the rainy season.
• The ozone layer’s thickness is measured in Dobson Units (DU), where 1 DU corresponds to a thickness of 0.01 mm of pure ozone gas at a temperature of 0°C and a pressure of 1 atm.
• These measurements help monitor the health and changes in the ozone layer over time.

Correct Answer is C.

• Chlorofluorocarbons (CFCs) are non-toxic, nonflammable chemicals composed of carbon, chlorine, and fluorine atoms.
• These compounds have been widely used in various industries, including as propellants in aerosol sprays, blowing agents for foams and packing materials, solvents, and refrigerants.
• One common CFC, trichlorofluoromethane (CFC-11), is effective at dissolving grease and is used to clean electronic equipment. Due to its high stability, CFCs can remain in the atmosphere for 80 to 100 years, making them significant contributors to ozone depletion when they break down in the stratosphere.
• The chlorine released from CFCs catalyzes the destruction of ozone molecules, leading to thinning of the ozone layer.

Correct Answer is D.

• Chlorofluorocarbons (CFCs), halons, and carbon tetrachloride are all ozone-depleting substances (ODS) that significantly contribute to the breakdown of the ozone layer.
• These chemicals were widely used in various applications, such as refrigeration, air conditioning, fire extinguishers, and industrial cleaning.
• However, due to their harmful effects on the ozone layer, the production and consumption of these substances were phased out following the Montreal Protocol.
• This international treaty, adopted in 1987 and enforced starting in 1989, successfully led to the global ban on many of these ozone-depleting substances, contributing to the protection and gradual recovery of the ozone layer.

Correct Answer is B.

• Chlorofluorocarbons (CFCs), halons, and carbon tetrachloride are ozone-depleting substances (ODS) that release chlorine particles into the atmosphere.
• These chlorine particles significantly contribute to the breakdown of the ozone layer. When these chemicals are released, they undergo chemical reactions in the stratosphere that lead to the formation of chlorine radicals, which then break down ozone molecules.
• The presence of these chlorine particles is also a major factor in the formation of the ozone hole, particularly over Antarctica.
• Due to their harmful effects on the ozone layer, the production and consumption of these substances were phased out under the Montreal Protocol, adopted in 1987 and enforced from 1989, resulting in a global ban and aiding the protection and gradual recovery of the ozone layer.

Correct Answer is B.

• The gases used in refrigerators are often sold under the brand name Mafron, and they are typically halonic hydrocarbons, which are a type of ozone-depleting substance.
• These gases, such as chlorofluorocarbons (CFCs) or hydrochlorofluorocarbons (HCFCs), have been widely used for refrigeration due to their stability and cooling efficiency.
• However, due to their harmful effects on the ozone layer, their use has been phased out under the Montreal Protocol. In contrast, ammonia is also used as a coolant in large industrial refrigeration systems, offering a more environmentally friendly alternative, as it does not contribute to ozone depletion.

Correct Answer is D.

• The ozone hole over Antarctica was first discovered by a British research team in 1985 using the Total Ozone Mapping Spectrometer (TOMS).
• This satellite-based instrument allowed scientists to observe and measure the depletion of ozone in the stratosphere. The discovery revealed the alarming thinning of the ozone layer over the Antarctic region, sparking international concern and leading to further research on the causes and consequences of ozone depletion.
• This finding ultimately contributed to the adoption of the Montreal Protocol in 1987 to phase out ozone-depleting substances and protect the ozone layer.

Correct Answer is C.

• In 2005, under the leadership of G.W. Kent Moore from the University of Toronto, researchers discovered an ozone hole over the Tibetan Plateau.
• This finding was significant because it revealed that ozone depletion was not limited to the polar regions, such as Antarctica, but was also occurring in other parts of the world.
• The research highlighted the vulnerability of the ozone layer in high-altitude areas and raised concerns about the potential impacts on ecosystems and human health in these regions.
• This discovery further emphasized the global nature of ozone depletion and the importance of continued efforts to protect the ozone layer.

Correct Answer is A.

• The ozone layer is a layer in Earth’s atmosphere that contains relatively high concentrations of ozone (O₃).
• It plays a critical role by absorbing 93-99% of the sun’s high-frequency ultraviolet (UV) light, which can be harmful to life on Earth, particularly by causing skin cancer, cataracts, and damaging ecosystems.
• Therefore, both the assertion and reason are true, and the reason (R) correctly explains the assertion (A). However, it is important to note that ozone, when considered as a gas at ground level, can be harmful to biotic life because it is toxic and can cause respiratory issues and other health problems.

Correct Answer is B.

• Chlorofluorocarbons (CFCs) are indeed the primary cause of ozone depletion. When released into the atmosphere, CFCs break down in the stratosphere, releasing chlorine atoms that destroy ozone molecules, leading to thinning of the ozone layer.
• Sulfur dioxide (SO₂) and nitrogen oxides (NOx) are major contributors to acid rain, not nitric acid. These gases react with water vapor in the atmosphere to form sulfuric and nitric acids, which then fall to the Earth’s surface as acid rain, affecting soil, water quality, and vegetation.
• Rocket fuel, often a highly refined form of kerosene, is used in some space missions, where its energy density and combustion characteristics are essential for propulsion.
• As for the greenhouse effect, carbon dioxide (CO₂) is the second-largest contributor after water vapor. While water vapor plays a key role in regulating Earth’s temperature, CO₂, along with other greenhouse gases like methane, traps heat in the atmosphere, contributing to global warming and climate change.