Optimized results of the K2-A2 models (see Table 2) with opacity increases (see Eqs. 2 and 3). Top: χ² values with N = 6 as a function of the opacity increase parameter, A₂. Bottom: Sound speed profile of models with A₂ = 0, 3, 5, 8, 10, 12, 14, 16, 18, and 20% at the solar age, compared with helioseismic data in Basu et al. (2009), c_s,obs. The model with our preferred value, A₂ = 10%, is highlighted with the thick line. The dashed line illustrates the shape of the δ_κ function with an arbitrary +0.006 vertical shift.