IUCN stands for:

International Union for Conservation of Nature and Natural Resources

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

IUCN is the world’s oldest and largest global environmental organization. Known for maintaining the IUCN Red List, which assesses the conservation status of plant and animal species. 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.

Note: The organisation is commonly referred to today as the “International Union for Conservation of Nature.” However, the abbreviation IUCN was originally expanded as “International Union for Conservation of Nature and Natural Resources,” which is the full traditional name associated with the acronym.