The wavelength of the energy emitted when an electron transitions from the fourth orbit to the second orbit in a hydrogen atom is $20.397 \, cm$. The wavelength of the energy for the same transition in $He^+$ is .......... $cm$.

  • A
    $5.099$
  • B
    $20.497$
  • C
    $40.994$
  • D
    $81.988$

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