Question

The ratio of the wavelengths for 2 → 1 transition in Li⁺⁺, He⁺ and H is

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

Answer 1

Answer: (C)

4 : : 36

Answer 2

Using $\frac{1}{\lambda} = RZ^{2}\left( \frac{1}{n_{1}^{2}} - \frac{1}{n_{2}^{2}} \right)$ ⇒ $\lambda \propto \frac{1}{Z^{2}}$

⇒ $\lambda_{Li}:\lambda_{He^{+}}:\lambda_{H} = \frac{1}{9}:\frac{1}{4}:\frac{1}{1} = 4:9:36$