B maj7/C#
The B maj7 chord consists of the B (Perfect unison), D# (Major third), F# (Perfect fifth) and A# (Major seventh) notes, with C# as the bass note.

How to play the B maj7/C# chord
- Play C# as the lowest bass note in the left hand
- Find B (Root) on the piano keyboard
- Add D# (Major third) — 4 semitones above B
- Add F# (Perfect fifth) — 7 semitones above B
- Add A# (Major seventh) — 11 semitones above B
- Press all 5 notes simultaneously to sound the B maj7/C# chord