Identify the incorrectly matched pairs.

The correct option is C 3 and 4
Ultraviolet (UV) radiation is a form of non-ionizing radiation emitted by the sun.

The UV radiations are of three types:

• UV-A: It has a wavelength range between 320 - 400 nm. It is not absorbed by the ozone layer and reaches the earth's surface. UV-A can penetrate into the deeper layers of the skin (both epidermis and dermis) and is responsible for the immediate tanning effect.
• UV-B: It has a wavelength range of 290 - 320 nm. Most of the UV-B is filtered by the ozone layer, yet some part of it reaches the earth's surface. It can penetrate only up to the epidermis of skin, damage DNA and cause mutation. It also causes aging of skin, damage to cells of skin, skin cancer and snow blindness in humans. Inflammation of the cornea due to the absorption of high doses of UV-B is called snow-blindness. This can damage the cornea permanently. However, UV-B cannot penetrate into the subcutaneous tissue.
• UV-C: It has a wavelength of 200 - 290 nm. It is absorbed by the ozone layer and does not reach the earth's surface given that the ozone layer is intact.

Hence, the ozone layer present in the stratosphere absorbs almost all of the sun's harmful ultraviolet light. It acts as a shield absorbing ultraviolet radiation from the sun.

However, the stratospheric ozone is depleted by pollutants called chlorofluorocarbons (CFCs), due to which the ozone layer is becoming thin. The Dobson Unit (DU) is the unit of measurement of thickness of the ozone in a column of air from the ground to the top of the atmosphere.

CFCs are used in the manufacture of aerosol sprays, blowing agents for foams and as refrigerants (coolants). CFCs discharged in the lower part of the atmosphere move upward and reach the stratosphere. In the stratosphere, UV rays act on them releasing chlorine atoms. Chlorine acts as a catalyst (Cl atoms are not consumed in the reaction) and degrades ozone, releasing molecular oxygen.