The Ramsar Convention on the conservation of wetlands came into force in:

The Convention on Wetlands of International Importance, especially as Waterfowl Habitat, is known as the Ramsar Convention. It was signed on 2 February 1971 in the city of Ramsar, in Iran, on the shores of the Caspian Sea, and came into force on 21 December 1975. It is one of the oldest intergovernmental environmental agreements. The date of its signing, 2 February, is celebrated every year as World Wetlands Day.

The Convention aims at the conservation and "wise use" of all wetlands through local and national action and international cooperation. Wetlands include marshes, swamps, lakes, rivers, mangroves, coral reefs, peatlands, rice paddies and even areas of sea water up to six metres deep at low tide. They are important for biodiversity, water purification, flood control, groundwater recharge, fisheries and carbon storage.

Each member country designates important wetlands in its territory for the "List of Wetlands of International Importance", called Ramsar sites. The Montreux Record lists Ramsar sites where changes in ecological character have occurred or are likely, due to human activity. India's Keoladeo National Park (Rajasthan) and Loktak Lake (Manipur) are on the Montreux Record.

India joined the Ramsar Convention on 1 February 1982. Its first two Ramsar sites were Chilika Lake (Odisha) and Keoladeo National Park (Rajasthan), both designated in 1981. India has rapidly increased its number of Ramsar sites in recent years, to more than 90, the largest number in Asia. Tamil Nadu has the most Ramsar sites among Indian states. The Sundarbans Wetland in West Bengal is India's largest Ramsar site by area.

Why not the other options?

• ✗1971 is the year the Convention was signed, not when it came into force.
• ✗1982 is the year India joined the Convention.
• ✗1992 is the year of the Rio Earth Summit.