Red Data Book is maintained by:

The correct answer is Option (3) → IUCN

The Red Data Book (now the IUCN Red List) is a record of species that have become extinct or are threatened with extinction. It is kept by the IUCN, the International Union for Conservation of Nature. The IUCN Red List (2004) records the extinction of 784 species in the last 500 years.

(1) WWF — Incorrect. The World Wide Fund for Nature is an organisation that works for nature conservation. It does not keep the Red Data Book.

(2) ICBN — Incorrect. The International Code of Botanical Nomenclature gives the rules for naming plants.

(3) IUCN — Correct. IUCN is the International Union for Conservation of Nature. It keeps the Red Data Book, the record of extinct and threatened species.

(4) ICZN — Incorrect. The International Code of Zoological Nomenclature gives the rules for naming animals.