Explanation:

- World Ozone Day, also known as the International Day for the Preservation of the Ozone Layer, is observed annually to raise awareness about the importance of the ozone layer and its preservation.

- Option:1, 8 September: No significant global observance related to the ozone layer falls on this date.

- Option:2, 16 September: Correct! World Ozone Day is celebrated on 16 September each year. This date marks the signing of the Montreal Protocol in 1987, a crucial international agreement aimed at phasing out substances that harm the ozone layer.

- Option:3, 12 September: Similar to option 1, there is no relevant observance for this date related to the ozone layer.

- Option:4, 6 September: Again, this date is not associated with any key event concerning the ozone layer.