Which chord is played at the 4th fret of the 2nd string?

The chord played at the 4th fret of the 2nd string is indeed Dmaj. On a guitar, the 2nd string is tuned to B. When you press down on the 4th fret, you are playing an E note. The D major chord is constructed from the notes D, F#, and A. However, if you are also playing the 2nd string at the 4th fret while playing a Dmaj chord shape, it adds the 3rd of the chord, which is F#. This results in the full Dmaj chord being present.

In terms of the other choices, D is typically played with the open 2nd string, making the note B part of the chord instead of the note E. G and Em chords do not correlate directly with the 4th fret of the 2nd string in the context of their standard shapes, as both chords use other frets and strings. Thus, Dmaj aligns perfectly as it utilizes the 4th fret on the 2nd string effectively, leading to the correct identification of the chord being played.