The UNESCO declared 2011 as the International Year of :

International Year of Biodiversity
International Year of Youth
International Year of Chemistry
Elderly Persons

The correct answer is: D. Elderly Persons

The United Nations Educational, Scientific and Cultural Organization (UNESCO) declared 2011 as the International Year of the Elderly Persons. The year was dedicated to promoting the well-being and rights of older persons and to raising awareness of the challenges they face.

The year 2011 was also the International Year of Chemistry. The year was dedicated to celebrating the achievements of chemistry and to promoting its role in solving global challenges.

The year 2011 was not the International Year of Biodiversity or the International Year of Youth.