Question

The minimum distance between particles in a wave that have the same displacement and are moving in the same direction is called?

Answer 1

A wavelength

Answer 2

Perhaps you need the Greek letter, Lambda

Answer 3

The question is poorly worded. For a planar wavefront, adjacent molecules in the same wave, in a direction perpendicular to wave travel, have the same displacement and direction.

So the wavelength is not the minimum distance between such particles or molecules.

Nevertheless, they are probably expecting the answer given by Damon.