The headquarters of the International Atomic Energy Agency (IAEA) is located in which city?

Introduction / Context:
The International Atomic Energy Agency (IAEA) plays a crucial role in monitoring nuclear activities and promoting the peaceful use of atomic energy. Because it is so important in global security and nuclear regulation, many general knowledge questions ask about the city where this organisation is headquartered.

Given Data / Assumptions:

• The question asks for the city that hosts the IAEA headquarters.
• Options: London, Vienna, an option suggesting a city in Paraguay and Washington, D.C.
• The IAEA is known to be based in Europe in a city that hosts several UN related bodies.

Concept / Approach:
As discussed in similar questions, the IAEA is headquartered in Vienna, Austria. Vienna is one of the main UN cities, alongside New York, Geneva and Nairobi. London and Washington, D.C. are capitals of major powers but are not the location of the IAEA's main offices. The reference to a city in Paraguay is clearly incorrect for this organisation, which is firmly associated with the Vienna International Centre.

Step-by-Step Solution:
Step 1: Recall the fixed association "IAEA – Vienna" from exam preparation material. Step 2: Recognise that Vienna is a European city that hosts multiple international organisations, including the IAEA. Step 3: Observe that London and Washington, D.C. are important but not linked to IAEA headquarters in standard references. Step 4: Note that a Paraguay based option does not match any well known description of the IAEA headquarters. Step 5: Select Vienna as the correct answer.

Verification / Alternative check:
Consulting official information about the IAEA will show that it is based in the Vienna International Centre in Austria. Many UN system diagrams label Vienna as a major hub of UN related agencies, with the IAEA as one of the most prominent among them. This confirms that Vienna is the correct headquarters city.

Why Other Options Are Wrong:
London: Although London is an important international city, it is not the official seat of the IAEA.
Paraguay City: Paraguay does not host the IAEA headquarters; this option appears only as a distractor.
Washington, D.C.: Washington is the capital of the United States and hosts other international institutions but not the IAEA headquarters.

Common Pitfalls:
Some learners may confuse the headquarters of the IAEA with those of other international bodies or assume that a powerful country like the United States must host every major organisation. To avoid this, memorise a short list of pairings such as "IAEA – Vienna", "UNESCO – Paris" and "FAO – Rome" so that different agencies are clearly separated in your mind.

Final Answer:
The headquarters of the International Atomic Energy Agency (IAEA) is located in Vienna.