Set 1 | Important Ozone Layer MCQs

Correct Answer is B.

• The Earth’s atmosphere is composed of multiple layers, each serving a crucial function. The stratosphere, which spans approximately 10 to 50 kilometers above the surface, contains the ozone layer primarily in its lower portion, between 15 and 30 kilometers.
• This layer, though its thickness varies by season and location, plays a vital role in shielding the Earth from the Sun’s harmful UV rays. While 90% of the ozone is concentrated in the stratosphere, the remaining 10% is found in the troposphere.

Correct Answer is D.

• The ozone layer is primarily located in the stratosphere, roughly 15 to 30 kilometers above the Earth’s surface, though its distribution is not uniform.
• Its density varies seasonally, being thicker during spring and thinner during autumn due to natural processes and human activities. Geographically, the ozone layer is more concentrated over the poles and less dense near the equator.
• This layer plays a critical role in absorbing the Sun’s harmful ultraviolet (UV) radiation, particularly UV-B and UV-C rays, protecting living organisms from potential DNA damage and various health issues such as skin cancer and cataracts.
• Additionally, about 90% of atmospheric ozone is concentrated in the stratosphere, while the remaining 10% exists in the troposphere, contributing to air quality and influencing weather patterns.

Correct Answer is D.

• The lowest layer of the atmosphere is known as the troposphere. It is thickest at the equator, extending up to 18–20 kilometers, and thins out near the polar regions.
• Above the troposphere are the stratosphere, mesosphere, thermosphere, and exosphere, arranged in ascending order. Each layer has distinct characteristics and plays a unique role in Earth’s atmospheric system.

Correct Answer is B.

• Chlorofluorocarbons (CFCs) are organic compounds composed of carbon, chlorine, and fluorine. Chlorine, a key element in CFCs, can under certain conditions break down ozone molecules in the stratosphere.
• This process significantly depletes the ozone layer, reducing its ability to shield the Earth from harmful ultraviolet radiation. Additionally, CFCs are potent greenhouse gases, contributing to global warming and making them a major factor in the greenhouse effect.

Correct Answer is D.

• Chlorofluorocarbons (CFCs) are a primary contributor to the depletion of the ozone layer, leading to the formation of the ozone hole. When CFCs are released into the atmosphere, they eventually reach the stratosphere, where they are broken down by ultraviolet radiation.
• This process releases chlorine atoms, which react with ozone molecules, causing their destruction. Over time, this depletion has resulted in a significant thinning of the ozone layer, particularly over Antarctica, creating what is commonly referred to as the “ozone hole.”

Correct Answer is C.

• Ozone (O₃) is a molecule composed of three oxygen atoms, distinct from O₂, the form of oxygen vital for aerobic life. While ozone is toxic and harmful at ground level, it serves a critical protective role in the upper atmosphere.
• In the stratosphere, the ozone layer acts as a shield, absorbing and blocking the Sun’s harmful ultraviolet (UV) radiation. Without this protection, UV radiation could severely harm living organisms, causing issues such as skin cancer in humans and damaging ecosystems.
  
  

Correct Answer is C.

• Stratospheric ozone is formed naturally through a series of chemical reactions driven by solar ultraviolet (UV) radiation and oxygen molecules.
• When UV rays strike oxygen molecules (O₂), they split into individual oxygen atoms (O). These free oxygen atoms then react with other O₂ molecules to form ozone (O₃).
• This continuous process, known as the ozone-oxygen cycle, maintains the ozone layer, which plays a crucial role in absorbing harmful UV radiation from the Sun.

Correct Answer is B.

• The ozone layer is vital to humanity because it acts as a protective shield, absorbing and filtering out the Sun’s harmful ultraviolet (UV) radiation, particularly UV-B and UV-C rays.

Correct Answer is D.

• Ultraviolet (UV) radiation from the Sun can cause skin cancer due to prolonged exposure, which may lead to genetic mutations in skin cells.
• UV rays are classified into three types: UV-A, UV-B, and UV-C. UV-A and UV-B rays are harmful to the skin, with UV-B being more potent in causing sunburns and DNA damage. UV-C, while extremely dangerous, is completely absorbed by the Earth’s atmosphere and does not reach the surface, thanks to the protective role of the ozone layer.
• This highlights the importance of shielding ourselves from UV-A and UV-B rays through protective measures like sunscreen and clothing.

Correct Answer is A.

• Ozone Layer Preservation Day, also known as World Ozone Day, is celebrated on September 16th each year. This day commemorates the signing of the Montreal Protocol in 1987, an international treaty aimed at phasing out the use of ozone-depleting substances to protect the ozone layer.
• The day serves as a reminder of the importance of preserving the ozone layer and raising awareness about the environmental impact of human activities.