Question

what should be the wavelength of a wave associated with a macroscopic body at rest or i may put it like this can we apply de broglies concept to bodies at rest

Answer 1

u should apply debroglies concept

Answer 2

de broglie introduced the concept of wavelength for matter(any body having a mass can be macroscopic also)
i think u know his eqn which includes mass
when
when a body is at rest the wavelength for such a body becomes undefined as there is no path taken by it to acquire a wavelength associated with its motion
when we dont have motion at the first place