Final answer:
A duet composed by Wolfgang Amadeus Mozart is most likely part of an opera, as his famous duets are typically found within the context of his larger operatic works.
Step-by-step explanation:
If the composer is Wolfgang Amadeus Mozart and the piece in question is a duet, it is likely part of an opera. While Mozart was prolific and composed works in many forms, including concertos, symphonies, and sonatas, his duets are most famously found within his operas, which are larger works that encompass both instrumental and vocal music performed on stage with a dramatic narrative.
In an opera, the music, acting, and often dance are combined to tell a story. Operas typically feature multiple characters, a storyline, and are performed with costumes and sets on a stage.