World Ozone day is celebrated on

The correct answer is A) 16 September. World Ozone Day marks the date in 1987 when the Montreal Protocol on Substances that Deplete the Ozone Layer was signed. The UN General Assembly formally proclaimed the day in 1994.

Why the others fail:

• B) 21 April: No ozone-related observance falls on this date.
• C) 25 December: This is Christmas, not an environmental observance.
• D) 30 January: In India this is Martyrs' Day, which honours Mahatma Gandhi.

The core concept is the stratospheric ozone layer, which shields life from harmful UV-B radiation, and the Montreal Protocol that phased out CFCs and other ozone-depleting substances. For Mains, the link is the Kigali Amendment (2016), which extended the regime to HFCs, a potent greenhouse gas. India ratified it in 2021, so this sits well in GS-III environment answers on climate and ozone governance.

Trap: Aspirants mix up World Ozone Day with World Environment Day (5 June) or Earth Day (22 April). Remember that the ozone day is tied to the Montreal Protocol, signed on 16 September 1987.