A hydrogen atom is in an excited state of principle quantum  number n. It emits a photon of wavelength $\lambda$ when it returns to the ground state. The value of n is

• A

  $\sqrt{\lambda R(\lambda R-1)}$

• B

  $\sqrt{\frac{\lambda (R-1)}{\lambda R}}$

• C

  $\sqrt{\frac{\lambda R}{\lambda R-1}}$

• D

  $\sqrt{\lambda (R-1)}$