Final answer:
The 1st movement of Eine kleine Nachtmusik is in the key of G major, uses Sonata Allegro form, has an Allegro tempo, is in 2/4 meter, and opens with a fortissimo dynamic.
Step-by-step explanation:
The key, form, tempo, meter, and opening dynamic of the 1st movement in Eine kleine Nachtmusik are as follows: The key is G major, which provides a bright and spirited foundation for the piece. The form is Sonata Allegro, a common form used in the classical period which includes an exposition, development, and recapitulation sections. The tempo marked is Allegro, indicating a brisk and lively pace.
The meter is 2/4, which gives the music its characteristic march-like rhythm. Finally, the opening dynamic is fortissimo (ff), starting the piece with strong and powerful energy immediately capturing the listener's attention.