Answer : 3. "Vienna"
Explanation :

The headquarters of the United Nations Industrial Development Organization (UNIDO) is situated in Vienna, Austria. UNIDO is a specialized agency of the United Nations that focuses on promoting and accelerating industrial development in developing countries. It works to enhance economic growth, reduce poverty, and improve living standards by fostering sustainable industrialization. The choice of Vienna as the headquarters reflects the city's historical significance as an international diplomatic and organizational hub.