To solve this problem, we need to identify the correct date for World Ozone Day from the given options.$\newline$World Ozone Day is celebrated to commemorate the signing of the Montreal Protocol on Substances that Deplete the Ozone Layer.$\newline$Let's analyze the options:$\newline \bullet$Option 1: 16th September - This is the correct date for World Ozone Day.$\newline \bullet$Option 2: 21st April - This date is not related to World Ozone Day.$\newline \bullet$Option 3: 5th June - This date is celebrated as World Environment Day, not World Ozone Day.$\newline \bullet$Option 4: 22nd April - This date is celebrated as Earth Day, not World Ozone Day.$\newline$Therefore, the correct option is Option 1: 16th September.