Correct Option: A

Three forms (or allotropes) of oxygen are involved in the ozone-oxygen cycle: oxygen atoms (O or atomic oxygen), oxygen gas (O2 or diatomic oxygen), and ozone gas (O3 or triatomic oxygen). Ozone is formed in the stratosphere when oxygen molecules photodissociate after absorbing an ultraviolet photon whose wavelength is shorter than 240 nm. This converts a single O2 into two atomic oxygen radicals. The atomic oxygen radicals then combine with separate O2 molecules to create two O3 molecules. These ozone molecules absorb UV light between 310 and 200 nm, following which ozone splits into a molecule of O2 and an oxygen atom. The oxygen atom then joins up with an oxygen molecule to regenerate ozone. This is a continuing process which terminates when an oxygen atom “recombines” with an ozone molecule to make two O2 molecules.