The energies of energy levels $\mathrm{A}, \mathrm{B}$ and $\mathrm{C}$ for a given atom are in the sequence $\mathrm{E}_{\mathrm{A}}<\mathrm{E}_{\mathrm{B}}<\mathrm{E}_{\mathrm{C}}$. If the radiations of wavelengths $\lambda_{1}, \lambda_{2}$ and $\lambda_{3}$ are emitted due to the atomic transitions $\mathrm{C}$ to $\mathrm{B}, \mathrm{B}$ to A and $C$ to A respectively then which of the following relations is correct?

• A

  $\lambda_{1}+\lambda_{2}+\lambda_{3}=0$
• B

  $\lambda_{3}=\lambda_{1}^{2}+\lambda_{2}$
• C

  $\lambda_{3}=\lambda_{1}+\lambda_{2}$
• Correct answer
  D

  $\lambda_{3}=\frac{\lambda_{1} \lambda_{2}}{\lambda_{1}+\lambda_{2}}$

Hence, the correct answer is option: 'D'.