Find the ratio of minimum to maximum wavelength of radiation emitted by electron in ground state of Bohr's hydrogen atom.

Minimum wavelength is corresponding to transition from $\mathrm{\infty }\to 1$ hence

${\lambda }_{min}=\frac{12431}{13.6}\text{Å}$

and maximum wavelength is for transition 2 $\to$ 1

$\Rightarrow {\lambda }_{max}=\frac{12431}{10.2}\text{Å}\Rightarrow \frac{{\lambda }_{min}}{{\lambda }_{\mathrm{ma}x}}=\frac{3}{4}$