Energy of incident radiation is given by: E=λhc​=300×10−96.64×10−34×3×108​=6.64×10−19=4.05 eV The work function of the metal is equal to 2.54 eV Hence the maximum kinetic energy of an ejected photoelectron would be 1.59 eV And the stopping potential needed to stop this would be 1.59 V.