Saha-Boltzmann (SB) line extinction coefficient against temperature at the centers of Lyα, Hα and Ca II 8542 Å (solid) and SB continuous extinction coefficient of the H I free-free and bound-free contributions (dashed) and the H⁻ free-free contribution (dot-dashed) at three ALMA wavelengths (from left to right 0.35, 1.3 and 3.0 mm), for gas of solar composition with different total hydrogen densities (from top to bottom N_H = 10¹⁵,10¹³ and 10¹¹ cm^-3, corresponding to the bottom, middle and top of the ALC7 chromosphere). The horizontal line at y = −7 specifies optical thickness unity for a line of sight through a 100 km wide slab. The small panels underneath each extinction graph show the competing neutral hydrogen and electron densities (solid, particles cm^-3). The overlaid dotted curves starting at 10 000 K are coronal-equilibrium (CE) neutral hydrogen and proton densities from CHIANTI. The density scales have the same logarithmic unit (dex) size as the extinction scales to enable slope comparisons. The y-axis scales shift between rows for better curve visibility,