Answer
$\eta_{\text {th, } \max }=31.3 \%$
Work Step by Step
The maximum thermal efficiency of this thermoelectric generator is the Carnot efficiency, $$
\eta_{\text {th, } \max }=\eta_{\text {th, Carnot }}=1-\frac{T_L}{T_H}=1-\frac{550 \mathrm{R}}{800 \mathrm{R}}=31.3 \%
$$
