C# maj9/F
The C# maj9 chord consists of the C# (Perfect unison), F (Major third), G# (Perfect fifth), C (Major seventh) and D# (Major ninth) notes, with F as the bass note.

How to play the C# maj9/F chord
- Play F 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 C (Major seventh) — 11 semitones above C#
- Add D# (Major ninth) — 14 semitones above C#
- Press all 6 notes simultaneously to sound the C# maj9/F chord