In a standing wave pattern, which is formed by the interference of two waves of the same frequency traveling in opposite directions, the nodes and antinodes play important roles.
Nodes are the points of zero amplitude or displacement in a standing wave. Antinodes, on the other hand, are the points of maximum amplitude or displacement in a standing wave. The distance between two consecutive nodes or antinodes is equal to half a wavelength.
In a single wavelength, there will be one node at each end (at the boundaries) and one node in the center, making a total of two nodes. Similarly, there will be one antinode at each end and one antinode in the center, resulting in a total of three antinodes.
So, in a wavelength of a standing wave, there are three antinodes.