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

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