(A) Chancellor Duke Metternich
The Vienna Congress (1815) was hosted by the Austrian Chancellor Duke Metternich.
Source: Chapter 1, Section 2.3 – A New Conservatism after 1815
The passage directly states: "The Congress was hosted by the Austrian Chancellor Duke Metternich." The other options are distractors — Ernst Renan was a French thinker, William I was the German Emperor (1871), and Otto von Bismarck was Prussia's chief minister who unified Germany. For MCQs, always link the name to their specific role mentioned in the textbook.