The correct answer to the question is option 3: Rio de Janeiro. In 2020, UNESCO named Rio de Janeiro as the World Capital of Architecture. This designation was given to the city in recognition of its exceptional architectural heritage and commitment to the development and promotion of architectural culture.

Tokyo, mentioned in option 1, is a major city renowned for its modern architecture and urban planning, but it was not named the World Capital of Architecture for 2020.

Johannesburg in option 2 and New Delhi in option 4 were not designated as the World Capital of Architecture for 2020 by UNESCO.

It is important to note that the World Capital of Architecture designation is awarded by UNESCO every three years to a city that demonstrates exemplary architectural initiatives and achievements. The aim of this title is to highlight the importance of architecture in sustainable urban development and to encourage dialogue and cooperation in the architectural community.