Stokes Q/I profiles as a function of wavelength in the spectral ranges centered on the K I D₂ (left panel) and D₁ (right panel) lines. The RT calculations were carried out in the absence of a magnetic field. A comparison is shown between the calculations considering a two-term atomic model with HFS, both taking J-state interference into account (black curves) and neglecting it (blue curves), and the calculations considering two-level atomic models with HFS (red curves), in which there is no J-state interference by definition. Overlapping curves are dashed to enhance visibility.