The maximum velocity of an electron emitted by light of wavelength $\lambda$ incident on the surface of a metal of work function $\phi$ is [$h=$ Planck's constant,$m=$ mass of electron and $c=$ speed of light]

• A
  $\sqrt{\frac{2(h c+\lambda \phi)}{m \lambda}}$
• B
  $\frac{2(h c-\lambda \phi)}{m}$
• C
  $\sqrt{\frac{2(h c-\lambda \phi)}{m \lambda}}$
• D
  $\frac{2(h \lambda-\phi)}{m}$