Respuesta :
The singing of nonsense syllables during improvised solos is called Scat singing.
"Erlkonig" was composed by Franz Schubert (and Carl Czerny but it wasnt in the choices).
Hope these are correct :) have a great day
The answer to your first question is Scatting, or Scat Singing.
As for the second question, the composer is Franz Schubert.
Hope this helps!!!