Final answer:
The saxophone was the crucial solo instrument of the swing era, playing a significant role in big band music and being featured extensively in musical arrangements of that time.
Step-by-step explanation:
One of the most important solo instruments of the swing era was the saxophone. During this time, the saxophone became synonymous with the swing sound and big band music, featuring heavily in the arrangements and solos. Renowned saxophonists like Coleman Hawkins, Lester Young, and Benny Carter helped to solidify the instrument's central role in swing music.