= Solution
Room <temperature> corresponds to about 0.026 eV, or $2.6\times10^{-5}$ keV. Read the left-hand branch there and draw a horizontal line to the rising hot branch. The original graph gives a return <temperature> of order $\boxed{k_BT'\sim1\text{–}2\ \mathrm{keV}}$, with graph-reading uncertainty, not the <temperature> of minimum conductivity.
At full ionization $n_e=13\rho/(27m_u)\simeq7.8\times10^{29}$ m$^{-3}$. Inserting the inferred <temperature> into $N_D=(4\pi/3)n_e[\epsilon_0k_BT'/(n_ee^2)]^{3/2}$ gives a Debye-sphere occupancy of order $60$–$170$. This is much greater than one and supports a collective weak-coupling description more than the conductivity-minimum region does. The approximate collision-time formula and omitted <Coulomb logarithm> do not warrant forcing the entire plotted conductivity curve to have its exact prefactor.
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