Which one of the following is not correctly matched?

The correct answer is C. World No Tobacco Day is observed on 31 May, not 5 May, so this is the mismatch. It is led by the WHO and is used each year to highlight a theme on tobacco control.

• A (correct match): World Environment Day falls on 5 June. The UN marks it every year, and it was first celebrated in 1974 after the 1972 Stockholm Conference.
• B (correct match): Earth Day falls on 22 April. It began in the US in 1970 and is now observed globally.
• D (correct match): World Ozone Day falls on 16 September. It marks the signing of the Montreal Protocol on 16 September 1987.

The core concept is the set of international observance days and the bodies that anchor them. For Mains GS-3 (environment), link the Montreal Protocol to the Kigali Amendment on HFCs and to India's ozone-depleting substance phase-out commitments.

Trap: Aspirants often memorise dates in isolation and then guess when one looks familiar. Pair each day with its originating body or event, such as WHO for tobacco or the Montreal Protocol for ozone, and the wrong date stands out.