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

How to play the F dim/D# chord
- Play D# as the lowest bass note in the left hand
- Find F (Root) on the piano keyboard
- Add G# (Minor third) — 3 semitones above F
- Add B (Diminished fifth) — 6 semitones above F
- Press all 4 notes simultaneously to sound the F dim/D# chord