Chemistry - Atomic Structure Question with Solution | TestHub

$\frac{1}{\mathrm{\lambda }}={\mathrm{R}}_{\mathrm{H}}\left(\frac{1}{{\mathrm{n}}_1^2}-\frac{1}{{\mathrm{n}}_2^2}\right)$for the H-atom
For the Balmer series,
${\mathrm{n}}_1=2$and${\mathrm{n}}_2=5$(for the third line).
$\frac{1}{\mathrm{\lambda }}={\mathrm{R}}_{\mathrm{H}}\left(\frac{1}{2^2}-\frac{1}{5^2}\right)=\frac{21}{100}{\mathrm{R}}_{\mathrm{H}}$
So$\text{λ}\text{=}\frac{\text{100}}{{\text{21R}}_H}$