Previous Year Question

Ozone (O₃) present in the atmosphere absorbs harmful Ultraviolet Radiation (UV) from the Sun. Ozone is a Triatomic Form of Oxygen, with each molecule containing three oxygen atoms. Most atmospheric ozone is concentrated in the Stratosphere, approximately 15–35 kilometres above the Earth's surface, forming the Ozone Layer. This layer plays an important role in protecting living organisms by preventing harmful solar ultraviolet radiation from reaching the Earth's surface.

Ultraviolet Radiation is classified into three categories based on Wavelength—UV-A (315–400 nm), UV-B (280–315 nm), and UV-C (100–280 nm). Among these, UV-C has the highest energy and is extremely harmful to biological organisms. Atmospheric oxygen and ozone together absorb almost all UV-C radiation. The Ozone Layer also absorbs most UV-B radiation, whereas most UV-A radiation reaches the Earth's surface. Therefore, the Ozone Layer is described as the Earth's Natural Protective Shield.

The absorption of ultraviolet radiation by ozone is a Photochemical Process. When ozone molecules absorb sufficiently energetic UV radiation, they can decompose into an Oxygen Molecule (O₂) and an Oxygen Atom (O). The free oxygen atom can subsequently react with oxygen molecules to form ozone again. Thus, ozone formation and destruction occur continuously in the Stratosphere. Chlorofluorocarbons (CFCs) and Halons can release chlorine and bromine, which disturb this natural balance and accelerate Ozone Depletion.

Among the other options, Infrared Radiation is primarily associated with thermal radiation and the Greenhouse Effect, whereas Visible Light is the portion of the electromagnetic spectrum detectable by the human eye. Microwaves are electromagnetic waves with longer wavelengths, used in communication and other technological applications. Ozone also absorbs some infrared and visible radiation, but the principal protective function of the Ozone Layer is the absorption of harmful ultraviolet radiation. Depletion of the Ozone Layer can increase the amount of UV-B radiation reaching the Earth's surface, raising the risks of skin cancer, cataracts, and damage to ecosystems.