On what string is the 12th fret an octave higher than the open string?

The correct answer highlights an important concept in understanding the guitar neck and musical intervals. The 12th fret on any string is indeed an octave higher than the open string. This is because the frets on a guitar are spaced to represent half steps, and moving from the open string position to the 12th fret effectively covers all 12 semitones that make up an octave.

For any given string on the guitar, if you play the open note and then move up to the 12th fret, you will reach a pitch that is double the frequency of the original open string note. This principle applies uniformly across all six strings of the guitar, regardless of the specific note being played.

Understanding this octave relationship is key for guitarists when navigating the fretboard, improvising, and composing music. It emphasizes the importance of the layout of the guitar, allowing players to know that they can find the same note an octave higher simply by moving to the 12th fret of the same string.