C major / B sharp major
Tip : Why B sharp? The range of C has 7 notes: C D E F G A B. Between E and F, but also between B and C there is a difference of a semitone (one fret guitar).
Other notes have a gap of two semitones (two frets of guitar). To meet the same magnitude of differences: if the C scale is C sharp, the 7th note will be B sharp. NB: it will be the usual note C!