The answer is An antinode occurs at the open end of a resonant tube.
Why do we have anti-nodes at the open end of a tube? Waves can be reflected, not only at the closed end of a tube, but also at the open end of a tube. Reflection occurs at the open end of a tube as a consequence of a phenomenon called radiation impedance, which occurs when a tube suddenly opens into a much larger space. Movement of air particles is not inhibited as it is at the closed end of the tube and so wave reflection occurs without inversion and anti-nodes are created at the open end.
However At the open end of a closed pipe; however,both nodes and antinodes are possible to form depending on the wavelength of the sound waves as well as the pipe's length.