= Solution
<Opacity> is the extinction cross section per unit <mass> for radiation; a frequency-dependent value $\kappa_\nu$ gives $dI_\nu/ds=-\kappa_\nu\rho I_\nu$ when emission is considered separately. Stellar radiative diffusion generally uses an appropriately weighted <Rosseland mean opacity>. The associated local <mean free path> is of order $1/(\kappa\rho)$.
At sufficiently high <temperature> the material is highly ionized, and scattering by free <electrons> is often dominant for ordinary stellar <densities> and photon energies well below the <electron> rest <energy>. Bound-bound and bound-free absorption weaken as bound <electrons> disappear; free-free absorption can still matter depending on <temperature> and <density>. Thus “high <temperature>” does not fix the dominant <opacity> at every possible <density>. The next part explicitly imposes a Kramers absorption law as a separate scaling model.
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