ozone is known as o3 and not o2 because o2 is that oxygen which we can breath but o3 is very, when 3 atoms of oxygen is joined it forms o3 which is known as ozone and it is corrosive.

o splits from ozone because it absorbs ultraviolet rays and then it again combines to form o2.

one atom of oxygen usually doesn't appears in nature but 2 atoms of it is seen in the nature so o3 splits in o2.
2 3 2
copy cat you are rat
and why they form as o3 but not as o2\