Final answer:
The third movement of Haydn's Trumpet Concerto is in a 3/4 time signature, providing a waltz-like rhythm to the piece.
Step-by-step explanation:
The third movement of Haydn's Trumpet Concerto is characterized by a 3/4 time signature, which gives the movement a rhythmic foundation that can be described as a waltz-like meter. This meter adds to the elegant and rhythmic melodic lines that are a prominent feature of this movement, played with finesse by the trumpet soloist. The concerto is a staple in the classical trumpeter's repertoire and showcases the instrument's capabilities through rapid passages and thematic variations within the meter.