Photons of energy 2.4 eV and wavelength λ fall on a metal plate and release photoelectrons with a maximum velocity v. By decreasing λ by 50% the maximum velocity of photoelectrons becomes 3 v. The work function of the material of the metal plate is
1
2.1 eV
2
1.7 eV
3
2.8 eV
4
2.0 eV