The key of C major
C D E F G A B
No sharps or flats. Relative minor: The key of A minor.
The triads of the key
I
C | ii
Dm | iii
Em | IV
F | V
G | vi
Am | vii°
B° |
The seventh chords
Imaj7
Cmaj7 | ii7
Dm7 | iii7
Em7 | IVmaj7
Fmaj7 | V7
G7 | vi7
Am7 | viiø7
Bm7♭5 |
C major scale
Open it in the app: 6. Harmony, in C