Arrange the following events in chronological order and select the correct answer from the codes given below : I. Rio Earth Summit II. Publication of Brundtland Commission Report III. Enforcement of Montreal Protocol IV. Publication of 'The limit to Growth' Report

The correct sequence is IV, II, III, I, so option B is right. Here are the dates behind each event.

• IV, The Limits to Growth (1972): The Club of Rome report, using systems modelling, warned that unchecked growth in population and resource use would hit planetary limits. It is the earliest of the four.
• II, Brundtland Commission Report (1987): Published as 'Our Common Future', it introduced the definition of sustainable development, meeting present needs without compromising future generations.
• III, Montreal Protocol enforcement (1989): The protocol was signed in 1987 but entered into force on 1 January 1989. The question asks about enforcement, so 1989 is the date to use.
• I, Rio Earth Summit (1992): The UN Conference on Environment and Development led to the UNFCCC, the CBD and Agenda 21.

The core concept is the evolution of global environmental governance, from awareness of limits to treaty-based action. For Mains GS-III, this links to sustainable development and the environment-economy debate.

Trap: Aspirants often date the Montreal Protocol to 1987, the year it was signed. Enforcement came two years later, and that gap can flip the order against the Brundtland Report.