Given any musical instrument, when a note is played on the instrument, does the fundamental have only one node and 2 antinodes (Theoretically fundamental frequencies should have half wavelength)? If yes what factor in the instrument allows it to create such a wave(like length of string )?
In short, no. If you take a tube, closed at both ends (or opened at both ends, depending if you are talking about nodes of pressure, or nodes of displacements), the fundamental will indeed have an anti-node and two nodes.
However, there are instruments which are making the sound from tubes closed at one end (the organ for instance). In that case, the fundamental frequency will have one node, and one anti-node.