The correct answer is Vienna, the federal capital of Austria and the seat of the Austrian government, parliament and the official residence of the President. Vienna sits in the north-east of the country on the Danube river, close to the borders with Slovakia and Hungary, which historically made it a crossroads between Western and Central-Eastern Europe. It is Austria's largest city by a wide margin, home to roughly a quarter of the national population, and it hosts several major international bodies, including the United Nations Office at Vienna, OPEC's headquarters and the OSCE, a fact frequently tested alongside geography questions in competitive exams. Salzburg, offered as an alternative, is a smaller city near the German border famous as the birthplace of Wolfgang Amadeus Mozart and for the Salzburg Festival, but it has never served as the national capital. Graz, Austria's second-largest city, lies in the south-eastern state of Styria and is known for its well-preserved old town and engineering institutions, yet it too holds no capital status. Innsbruck, nestled in the Tyrolean Alps and twice a host of the Winter Olympics, is regionally important but administratively only the capital of the Tyrol state, not of Austria as a whole. A common exam confusion arises because candidates mix up Austria's largest, most photogenic, or most historically famous cities with its actual seat of government, especially since Salzburg and Innsbruck appear frequently in tourism-based questions. The safe revision takeaway is a simple one-to-one rule: Vienna is Austria's capital, largest city and diplomatic hub, while Salzburg, Graz and Innsbruck, despite their prominence, remain provincial capitals only. Memorising this alongside Austria's currency and neighbours consolidates a complete factual profile of the country for General Knowledge papers.