B 3/A#
The B 3 chord consists of the B (Perfect unison) and D# (Major third) notes, with A# as the bass note.

How to play the B 3/A# chord
- Play A# as the lowest bass note in the left hand
- Find B (Root) on the piano keyboard
- Add D# (Major third) — 4 semitones above B
- Press all 3 notes simultaneously to sound the B 3/A# chord