Question

The ratio of the wavelength for $2\to 1$ transition in ${Li}^{+},{He}^{+}$ and $H$ is :

• A. $1:2:3$
• B. $1:4:9$
• C. $4:9:36$
• D. $3:2:1$

Answer 1

Answer: (C)

$4:9:36$

Using $\frac{1}{\lambda }=R{Z}^2(\frac{1}{n_1^2}-\frac{1}{n_2^2})\Rightarrow \lambda \propto \frac{1}{Z^2}$

$\Rightarrow {\lambda }_{Li}:{\lambda }_{He}:{\lambda }_H=\frac{1}{9}:\frac{1}{4}:\frac{1}{1}=4:9:36$