The first United Nations Earth Summit on environment and sustainable development was held in which city?

Introduction / Context:
The term “Earth Summit” is commonly used for the United Nations Conference on Environment and Development, a landmark global meeting that brought sustainable development to the centre of international agendas. This question asks for the host city of the first major Earth Summit, which is an important fact in environmental and geography based general knowledge.

Given Data / Assumptions:

• The event is the first Earth Summit on environment and development.
• The options are Buenos Aires, Rio de Janeiro, Dar-es-Salaam and “None of these”.
• We assume reference to the 1992 summit formally known as UNCED.
• The task is to identify the famous host city.

Concept / Approach:
The 1992 Earth Summit was held in Rio de Janeiro, Brazil. It produced key international agreements such as the Convention on Biological Diversity and the Framework Convention on Climate Change, and it popularised the idea of sustainable development. Many exam questions simply ask “Earth Summit 1992 was held where?” so the name “Rio de Janeiro” becomes a must know fact.

Step-by-Step Solution:
Step 1: Recall that the famous Earth Summit linked with Agenda 21 and major environment treaties took place in Brazil.Step 2: Among the Brazilian cities listed in standard general knowledge, the relevant one is Rio de Janeiro, not Buenos Aires or Dar-es-Salaam.Step 3: Buenos Aires is the capital of Argentina and is not associated with the 1992 Earth Summit.Step 4: Dar-es-Salaam is in Tanzania and is not the city where the first major Earth Summit was held.Step 5: Therefore, the only correct option matching the well known fact is “Rio de Janeiro”.

Verification / Alternative check:
For verification, remember that when people talk about Earth Summit agreements, they often use phrases like “Rio Summit” or “Rio 1992”. Later conferences, such as Johannesburg 2002 and Rio+20 in 2012, also refer back to the original Rio meeting. This repeated association of the Earth Summit with the city of Rio de Janeiro confirms the answer.

Why Other Options Are Wrong:
Buenos Aires: Although an important Latin American city, it did not host the 1992 Earth Summit.

Dar-es-Salaam: A major city in Tanzania, but not linked with the first United Nations Earth Summit.

None of these: Incorrect because one of the listed options, Rio de Janeiro, is in fact the precise host city.

Common Pitfalls:
Sometimes candidates confuse the Earth Summit with other environmental meetings or with the earlier 1972 conference in Stockholm on the human environment. Another error is mixing up Latin American cities and wrongly picking Buenos Aires instead of Rio de Janeiro. Recalling the specific phrase “Rio Earth Summit 1992” is an effective way to avoid these mistakes.

Final Answer:
The first major United Nations Earth Summit on environment and development was held in Rio de Janeiro.