What is the key of progression

In tonal music, chord progressions have the function of establishing or contradicting a tonality, the technical name for what is commonly understood as the "key" of a song or piece. Chord progressions are usually expressed by Roman numerals in Classical music theory. For example, the common chord progression I–vi–ii–V.

Explanation:

the style of music that was composed during the classical era was concerto grosso.