In which country is the de capo aria most commonly found?

The de capo aria is most commonly associated with Italy, particularly during the Baroque period when it became a significant form in opera and vocal music. This type of aria follows a three-part structure, typically labeled A-B-A. The first section (A) introduces the main theme, which is often lyrical and expressive. The second section (B) contrasts the A section, usually featuring different music and often a different emotional mood. The return to the A section allows for embellishments and variations in the vocal line, showcasing the singer's virtuosity and providing a familiar resolution to the audience.

Italy was the heart of Baroque music development, where composers like Handel and Vivaldi utilized the de capo aria in their operas and cantatas, thus solidifying its prominence in the Italian musical tradition. This rich cultural context highlights the importance of the de capo aria in Italian opera and song, making it the correct choice for this question.