World Ozone Day' is celebrated on

The correct answer is C. World Ozone Day is observed on 16 September every year. The date marks the signing of the Montreal Protocol on Substances that Deplete the Ozone Layer in 1987. The UN General Assembly adopted 16 September as the observance date in 1994.

Why the others are wrong:

• A) 25 December is Christmas, with no link to ozone.
• B) 21 April has no ozone link. Earth Day is 22 April, which is a different observance.
• D) 30 January is Martyrs' Day in India, not an ozone-related date.

Core concept: the stratospheric ozone layer shields the earth from harmful UV-B radiation. CFCs and halons deplete it. The Vienna Convention (1985) created the framework, and the Montreal Protocol (1987) set binding phase-out schedules. India ratified both and is party to the Kigali Amendment (2016) on HFCs. For Mains GS-III, this is a model of successful multilateral environmental governance and a useful example when discussing climate agreements.

Trap: Candidates mix up the Vienna Convention date (22 March) with the Montreal Protocol date (16 September), or confuse ozone day with Earth Day.