A# 7/B
The A# 7 chord consists of the A# (Perfect unison), D (Major third), F (Perfect fifth) and G# (Minor seventh) notes, with B as the bass note.

How to play the A# 7/B chord
- Play B as the lowest bass note in the left hand
- Find A# (Root) on the piano keyboard
- Add D (Major third) — 4 semitones above A#
- Add F (Perfect fifth) — 7 semitones above A#
- Add G# (Minor seventh) — 10 semitones above A#
- Press all 5 notes simultaneously to sound the A# 7/B chord