What is the 1st fret note on the 2nd (B) string?

The first fret note on the second (B) string is C. This is determined by understanding the musical alphabet, which consists of the notes A through G, and the pattern of whole and half steps on the guitar.

The open B string is tuned to the note B. When you press down on the first fret, you raise the pitch of the string by a half step. Moving up one half step from B leads you to C. This is a foundational concept in learning the fretboard, as understanding how to find notes based on their position and the tuning of each string is essential for playing various scales, chords, and melodies on the guitar.

It's also useful to remember the natural notes on the fretboard and how they are spaced. For instance, between B and C, there is a half step, which reinforces the idea that pressing the first fret on the B string will give you the note C.