Answer
$7.88\times10^4 K$.
Work Step by Step
It takes 10.2 eV of energy to excite a hydrogen atom from the n = 1 state to the n = 2 state (page 791).
If the temperature of the H gas were high enough that the average kinetic energy of a hydrogen atom equaled that energy difference, the H atom would be excited.
Use equation 13–8.
$$KE=\frac{3}{2}kT$$
$$T=\frac{2KE}{3k}$$
$$=\frac{2(10.2eV)(1.60\times10^{-19}J/eV)}{3(1.38\times10^{-23}J/K)}$$
$$= 7.88\times10^4 K $$
