Fractional linear polarization Q/I profile for the core and near-wing region of the K line as a function of wavelength distance to the center of the line. The considered redistribution treatment is PRD, a horizontal magnetic field of B = 10 G is present and the emergent profiles are shown for the center of the solar disk, with μ = 1. The solid black and red curves correspond to calculations for 3L (neglecting metastable levels) and 5L (including the metastable levels) atomic models, respectively. The reference direction for positive Stokes Q is the perpendicular to the horizontal magnetic field.