IUCN stands for:

The correct answer is Option (3) → International Union for Conservation of Nature and Natural Resources

IUCN is the world body that assesses how many species exist and how threatened they are. It publishes the Red List of threatened species. Its full name has both ‘Nature’ and ‘Natural Resources’.

Option (3) International Union for Conservation of Nature and Natural Resources — Correct. IUCN is the International Union for Conservation of Nature and Natural Resources. Its Red List (2004) documents the extinction of 784 species in the last 500 years.

Note: A similar question was also asked in CUET (UG) 2026 on 26-05-2026 (Slot 1) and on 25-05-2026 (Slot 1).

NCERT Extract:
Biodiversity – “… Since there are published records of all the species discovered and named, we know how many species in all have been recorded so far, but it is not easy to answer the question of how many species there are on earth. According to the International Union for Conservation of Nature and Natural Resources (IUCN) (2004), the total number of plant and animal species described so far is slightly more than 1.5 million, but we have no clear idea of how many species are yet to be discovered and described.”