There is no such thing as B major. There is B minor and B flat major. The subdominant triad of B minor ( I'm pretty sure) is E minor.
A subdominant triad (Grade 5 Theory) is a triad built on the scale degree IV (four)
In a major key, the triad built on the 7th scale degree is diminished. Using C major as an example, the triad on the 7th is B D F. B to D is a minor 3rd, as is D to F, so B to F is a diminished 5th.
G,b,d
The augmented triad does not appear in any major or natural minor scales.
The note "A"
The subdominant triad of Eb major is the Ab major triad.
Subdominant. Its triad is major.
A subdominant triad (Grade 5 Theory) is a triad built on the scale degree IV (four)
F Major
The subdominant note of E-flat minor is A-flat.
The subdominant in any major scale is the fourth note. So, in C major, the subdominant is the F.
The subdominant in a scale is the 4th, which in the key of B-flat major is E-flat.
The subdominant note is D in an A major scale
b major
C major triad : C - E - GG major triad : G - B - DD major triad : D - F# - AA major triad: A - C# - EE major triad : E - G# - BB major triad : B - D# - FC# major triad: C# - E# - G#F# major triad : F# - A# - C#Cb major triad : Cb - Eb - GGb major triad : Gb - Bb - DbDb major triad : Db - F - AbAb major triad : Ab - C - EbEb major triad : Eb - G - BbBb major triad : Bb - D - FF major triad : F - A - CA natural minor triad : A - C - EE natural minor triad : E - G - BB natural minor triad : B - D - F#F# natural minor triad : F# - A - C#C# natural minor triad : C# - E - G#A# natural minor triad : A# - C# - EG# natural minor triad : G# - B - D#D# natural minor triad : D# - F# - A#Eb natural minor triad : Eb - Gb - BbAb natural minor triad : Ab - C -EbBb natural minor triad : Bb - Db - FD natural minor triad : D - F - AG natural minor triad : G - Bb - DC natural minor triad : C - Eb - GF natural minor triad : F - Ab - C
In a major key, the triad built on the 7th scale degree is diminished. Using C major as an example, the triad on the 7th is B D F. B to D is a minor 3rd, as is D to F, so B to F is a diminished 5th.
The subdominant note is the fourth scale degree of any key, for example in C major the subdominant note is F since the scale goes C D E F G A B C.