$A$ photo-emissive substance is illuminated with a radiation of wavelength $\lambda_i$ so that it releases electrons with de-Broglie wavelength $\lambda_c$. The longest wavelength of radiation that can emit photoelectrons is $\lambda_0$. The expression for the de-Broglie wavelength is given by ($m$: mass of the electron,$h$: Planck's constant,and $c$: speed of light).

• A
  $\lambda_c = \sqrt{\frac{h}{2mc \left(\frac{1}{\lambda_i} - \frac{1}{\lambda_0}\right)}}$
• B
  $\lambda_c = \sqrt{\frac{h\lambda_0}{2mc}}$
• C
  $\lambda_c = \frac{h}{\sqrt{2mc \left(\frac{1}{\lambda_i} - \frac{1}{\lambda_0}\right)}}$
• D
  $\lambda_c = \sqrt{\frac{h\lambda_i}{2mc}}$