The work function of a metal is 4ev. For emitting photo electron of zero velocity from the surface of this metal, The wave length of incident light required must be 

• A

  2700 $\stackrel{\mathrm{o}}{\mathrm{A}}$

• B

  1700 $\stackrel{\mathrm{o}}{\mathrm{A}}$

• C

  5900 $\stackrel{\mathrm{o}}{\mathrm{A}}$

• D

  3100 $\stackrel{\mathrm{o}}{\mathrm{A}}$