Question

In stratosphere most of the ozone formation is assisted by :

• A. \(\gamma\)-rays.
• B. visible radiations.
• C. ultraviolet radiation.
• D. cosmic rays.

Hint:

Remember the dual role of the ozone layer: it is formed by UV radiation, and it also protects life on Earth by absorbing most of the harmful incoming UV-B and UV-C radiation. This absorption is what leads to the destruction of ozone, creating a natural dynamic balance.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks about the primary type of radiation from the sun that drives the formation of ozone in the stratosphere.
Step 2: Detailed Explanation:
The formation and destruction of ozone in the stratosphere are described by the Chapman cycle. The formation process occurs in two main steps:
1. Photodissociation of Oxygen: An oxygen molecule (O\(_2\)) absorbs high-energy photons from sunlight and splits into two free oxygen atoms (O). The energy required for this corresponds to radiation with a wavelength of less than 242 nm, which falls in the ultraviolet (UV-C) part of the electromagnetic spectrum.
\[ \text{O}_2 + h\nu (\text{UV radiation}) \rightarrow \text{O} + \text{O} \] 2. Ozone Formation: Each of these highly reactive oxygen atoms then combines with another oxygen molecule to form a molecule of ozone (O\(_3\)). This reaction usually requires a third body (M), such as N\(_2\) or another O\(_2\) molecule, to carry away the excess energy.
\[ \text{O} + \text{O}_2 + \text{M} \rightarrow \text{O}_3 + \text{M} \] The crucial initiating step is the breaking of the O\(_2\) bond, which is powered by UV radiation. Visible light does not have enough energy per photon to do this, and while gamma rays and cosmic rays are highly energetic, their flux is much lower and they are not the primary drivers of this large-scale atmospheric process.
Step 3: Final Answer:
The formation of ozone in the stratosphere is primarily assisted by ultraviolet radiation.