First "Earth Summit" for "Convention on Biological Diversity" was held at -

The correct answer is Rio de Janeiro (1992), Brazil.

• The first "Earth Summit" for "Convention on Biological Diversity" was held at Rio de Janeiro (1992), Brazil.
• The Convention on Biological Diversity was signed at the Earth Summit in Rio de Janeiro, Brazil on 5th June 1992 and entered into force on 29 December 1993.
• It is an international legal instrument for "the conservation of biological diversity, the sustainable use of its components, and the fair and equitable sharing of the benefits arising out of the utilization of genetic resources".  
• The Secretariat of the Convention on Biological Diversity is based in Montreal, Canada.
• It is a legally binding treaty.