CBSE Questions for Class 11 Medical Chemistry Environmental Chemistry Quiz 11 - MCQExams.com

Ozone layer is formed in the stratosphere of the atmosphere by the action of UV rays on the oxygen molecules. This ozone layer acts as absorbant for the harmful UV radiations and so, these radiation do not cross the troposphere to reach the earth's surface. However, the ozone depleting pollutants like chlorofluorocarbons reach the stratosphere and break when exposed to the UV rays. This process releases the reactive chlorine which further reacts with ozone to form simple oxygen. That is how the ozone layer is depleted. Hence, the correct answer is 'Chlorofluorocarbons'.

•  The UV region covers the wavelength range 100-400 nm and is divided into three bands: UVA (315-400 nm) UVB (280-315 nm)
• The most common form of UV radiation is sunlight, which produces three main types of UV rays: UVA, UVB, UVC.
• At certain wavelengths, UV is mutagenic to bacteria, viruses and other microorganisms. Particularly at wavelengths around 260–270 nm, UV breaks molecular bonds within microorganismal DNA, producing thymine dimers that can kill or disable the organisms.
• UVB, the chief cause of skin reddening and sunburn, tends to damage the skin's more superficial epidermal layers. It plays a key role in the development of skin cancer and a contributory role in tanning and photoaging.

• CFCs and other halogenated ozone depleting substances (ODS) are mainly responsible for manmade chemical ozone depletion.
• The total amount of effective halogen (Chlorine and bromine) in the stratosphere can be calculated and are known as the equivalent effective stratospheric chlorine.

Peroxyacetyl nitrate is a secondary pollutant since they form in the atmosphere after the emission of primary pollutants. It is present in photochemical smog.

Surface water getting contaminated with PCB waste generally has high levels of PCBs in sediment, as the PCBs attach to organic matter. PCBs can be slowly released from the sediment into the water and evaporate into the air.

Sulfur dioxide another toxic chemical gas when combines with water and air, forms sulfuric acid, which is the main component of acid rain. Carbon dioxide in the air can dissolve in rainwater to form carbonic acid, $$H_{2}CO_{3}$$ and contributes to acid rain.

IR active molecules in the atmosphere can increase their vibrational energy by absorbing some of this infrared light, and thus increasing the temperature of the atmosphere resulting in Global warming.

The correct option is A.

Hint: Antarctica is the winter dominated continent which is covered with ice.

Correct Answer: Option (B).

Explanation:

The very low temperature in the Antarctic stratosphere form polar stratospheric clouds which contain Chlorine nitrate $$(ClNO_3)$$.

These polar stratospheric clouds cause the severe depletion of the Antarctic ozone layer known as the ozone hole.

Final Answer: In Antarctica, ozone depletion is due to the formation of Chlorine nitrate.