During which one of the following the Convention on Biodiversity was opened for signature?

Correct option is A

The Convention on Biological Diversity (CBD) was opened for signature during the Rio Summit, also known as the Earth Summit, which took place in Rio de Janeiro, Brazil, in 1992. The Rio Summit was a major international conference organized by the United Nations that focused on sustainable development and environmental issues. It led to several key agreements, including the CBD, which aims to conserve biological diversity, promote sustainable use of its components, and ensure fair and equitable sharing of benefits arising from genetic resources.
Information Booster:
 Stockholm Conference: Held in 1972, it was the United Nations Conference on the Human Environment. This conference led to the creation of the United Nations Environment Programme (UNEP) but did not focus specifically on biodiversity.
 Ramsar Convention: This is an international treaty for the conservation and sustainable use of wetlands, signed in Ramsar, Iran, in 1971. It does not specifically address biodiversity in the broader sense covered by the CBD.
 Montreal Protocol: Adopted in 1987, it is an international treaty designed to protect the ozone layer by phasing out the production of numerous substances responsible for ozone depletion. It does not deal with biodiversity.