Which circular structure is typically capped with a dome?

• A. Underglaze
• B. Rotunda
• C. Oculus
• D. Concrete

Answer: (B)

In architecture, a rotunda is a circular building whose defining feature is a domed roof. The name itself reflects the round plan, and the dome on top is the classic pairing you’d expect. That combination—round, open interior space capped by a dome—makes rotunda the best fit for a circular structure topped with a dome. A famous example is the Pantheon in Rome, and the U.S. Capitol’s central space is often referred to as the Rotunda because of its dome.

The other terms don’t describe a circular building topped by a dome. Underglaze is a type of glaze used on ceramics, not a building type. An oculus is a circular opening, usually in a wall or dome, not the entire structure. Concrete is a material used to construct buildings, not a structural form or roof type.