Ozone Day is celebrated on:

Correct answer: (a) 16 September

Explanation

The International Day for the Preservation of the Ozone Layer (World Ozone Day) is observed on 16 September. It marks the signing of the Montreal Protocol on 16 September 1987, which phases out ozone-depleting substances such as chlorofluorocarbons (CFCs).

• 5 June: World Environment Day;
• 21 April: Civil Services Day in India;
• 5 December: World Soil Day.