Final answer:
Mozart's Symphony No. 40 in G Minor, K. 550, III is a Menuetto in a compound ternary form, and it is in 3/4 time, adhering to the traditional dance form of the Classical period.
Step-by-step explanation:
The third movement of Mozart's Symphony No. 40 in G Minor, K. 550 is a Menuetto. This is a traditional dance form, typically in 3/4 time, which was common in symphonies during the Classical period. Regarding the form of the movement, it adheres to the typical structure of a menuetto, which is generally not in sonata-allegro, rondo, theme and variations, or aria form, but is its own distinct type with a trio section in the middle. However, specific to Mozart’s Symphony No. 40, the third movement's form can be considered a compound ternary or minuet and trio form.
As for the meter of the movement, it is indeed in 3/4 time, which is characteristic of the minuet dance form. This meter helps to give the movement its dance-like quality, with an accent on the first beat of each measure which is typical for a minuet.