Question

The longest wavelength line in the Lyman series of the hydrogen spectrum is

• A. $ 949.8\,?$
• B. $ 972.6\,?$
• C. $ 1215.8\,?$
• D. $ 1025.8\,?$

Answer 1

The Correct Option is C

$\frac{1}{\lambda} R_{H}\left[\frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}}\right]$
For longest wavelength in Lyman series,
$n_{1}=1, n_{2}=2 $
$\frac{1}{\lambda}=1.09678 \times 10^{7}\left[\frac{1}{(1)^{2}}-\frac{1}{(2)^{2}}\right] $
$\frac{1}{\lambda}=\frac{1.09678 \times 10^{7} \times 3}{4} $
$\therefore \lambda=1.2156 \times 10^{-7} \,m $
$=1215.6\,?$