music: 50's Chart Toppers: Name The Artist: With You On My Mind?

Questions

in motor racing, what is yellow?

in music, instrumental introduction to an opera or other musical or nonmusical dramatic work?

in music, the art of extemporization or creating all or part of a composition at the moment of performance?

in musical notation, what is the term for the symbol at the beginning of a staff?

in norse mythology, who is brunhilda chief of?