Stokes Q/I profile as a function of wavelength in the spectral range centered on the K I D₂ line. The RT calculations were carried out in the absence of a magnetic field and considering a two-term atomic model with HFS. For the figures shown in the rest of this work, PRD effects were taken into account in the line scattering emissivity unless otherwise noted. Calculations carried out neglecting the impact of depolarizing collisions (black curves) are compared to those in which the D⁽²⁾(J_u, F_u) rates were set to for all HFS levels with quantum number F ≥ 1 (red curves).