Question

The wavelength of the energy emitted when electron come from fourth orbit to second orbit in hydrogen is $ 20,397\text{ }c{{m}^{-1}} $ . The wavelength of energy for the same transition in He+ is :

• A. $ 81,988c{{m}^{-1}} $
• B. $ 40,994c{{m}^{-1}} $
• C. $ 20,497c{{m}^{-1}} $
• D. $ 5,099\text{ }c{{m}^{-1}} $

Answer 1

Answer: (D)

As $ \lambda \propto \frac{1}{{{Z}^{2}}} $ Hence wavelength of energy for same transition in He is, here Z = 2 hence, $ \frac{20397}{4}=5099\text{ }c{{m}^{-1}} $