* Đáp án
* Hướng dẫn giải
Do $E = - \frac{{13,6}}{{{n^2}}}$ eV và $\Delta {E_1} = {E_4} - {E_1} = \frac{{hc}}{{{\lambda _1}}};$
$\Delta {E_2} = {E_5} - {E_3} = \frac{{hc}}{{{\lambda _2}}}$ nên
$\frac{{{E_5} - {E_3}}}{{{E_4} - {E_1}}} = \frac{{{\lambda _1}}}{{{\lambda _2}}}$ $ \Leftrightarrow \frac{{ - \frac{{13,6}}{{{5^2}}} + \frac{{13,6}}{{{3^2}}}}}{{ - \frac{{13,6}}{{{4^2}}} + \frac{{13,6}}{{{1^2}}}}} = \frac{{{\lambda _1}}}{{{\lambda _2}}}$ $ \Leftrightarrow \frac{{256}}{{3375}} = \frac{{{\lambda _1}}}{{{\lambda _2}}} \Leftrightarrow 256{\lambda _2} = 3375{\lambda _1}.$