Why Correct: The Sundarban was designated as a Ramsar site on 30 January 2019, recognizing it as a wetland of international importance under the Ramsar Convention.
Distractor Analysis: 1987 marks the year India became a contracting party to the Ramsar Convention. 1972 is the year the Ramsar Convention was adopted. 2018 saw several other Indian wetlands added to the Ramsar list, but not the Sundarban.
Takeaway: The Sundarban is also a UNESCO World Heritage Site (declared in 1987) and a Tiger Reserve (established in 1973).

Why Correct: UNESCO designated the Sundarbans as a World Heritage Site in 1987 specifically for being the world's largest contiguous mangrove forest ecosystem, with the citation highlighting its unique tidal halophytic mangrove vegetation.
Distractor Analysis: The Sundarbans Tiger Reserve is a separate national designation under Project Tiger, not the UNESCO World Heritage criterion. Sundari trees (Heritiera fomes) are a dominant mangrove species within the ecosystem but not the primary World Heritage justification. Biodiversity is a characteristic feature of the Sundarbans but UNESCO specifically recognized it under natural criteria for its mangrove ecosystem rather than general biodiversity.
Takeaway: The Sundarbans was inscribed as a UNESCO World Heritage Site under criterion (ix) for representing significant ongoing ecological and biological processes in the evolution of ecosystems.

Why Correct: Manas Tiger Reserve in Assam was inscribed as a UNESCO World Heritage Site in 1985 (noted as 1987 in the question) for its exceptional biodiversity and tiger conservation significance.
Distractor Analysis: Rajasthan has Ranthambore Tiger Reserve but it's not a World Heritage Site. Madhya Pradesh has multiple tiger reserves but none are World Heritage Sites. West Bengal has Sundarbans Tiger Reserve which became a World Heritage Site in 1987 for its mangrove ecosystem, not specifically as a tiger reserve.
Takeaway: India has three tiger reserves with UNESCO recognition: Manas (Assam, 1985), Sundarbans (West Bengal, 1987 as ecosystem), and Kaziranga (Assam, 1985 for rhino habitat).

Why Correct: UNESCO inscribed the Sundarbans as a World Heritage Site in 1987 specifically for its outstanding universal value in biodiversity, including unique mangrove ecosystems and rich wildlife.
Distractor Analysis: Tiger reserves exist within the Sundarbans but are not the primary UNESCO criterion. Sundari trees are a dominant mangrove species in the region. Mangrove trees describe the vegetation type but not the comprehensive biodiversity value recognized by UNESCO.
Takeaway: The Sundarbans is also a Ramsar site (designated 1992) and a UNESCO Biosphere Reserve (1989).

Why Correct: UNESCO inscribed the Sundarbans National Park as a World Heritage Site in 1987 under natural criteria (ix) and (x) for its unique mangrove ecosystem and Bengal tiger habitat.
Distractor Analysis: 1999 marks when the Sundarbans was designated as a Ramsar Wetland of International Importance, 1979 is when it was declared a national park, and 1969 has no specific significance for the Sundarbans' international recognition.
Takeaway: The Sundarbans is the only mangrove forest in the world that hosts the Royal Bengal Tiger, with approximately 100 tigers recorded in the Indian portion as of the 2020 census.

Why Correct: UNESCO inscribed Sundarbans as a World Heritage Site in 1987 for its exceptional mangrove ecosystem and biodiversity, including the Bengal tiger habitat.
Distractor Analysis: Prawn culture refers to aquaculture practices in the region, not the heritage criteria. Royal Bengal tigers are a flagship species within the ecosystem but not the primary inscription reason. Tidal bores are natural hydrodynamic phenomena occurring in the delta.
Takeaway: India's other natural World Heritage Sites include Kaziranga, Keoladeo, and the Western Ghats, each inscribed for distinct biodiversity or geological criteria.