The work functions (in eV) of Mg, Cu, Ag, Na respectively are 3.7, 4.8, 4.3, 2.3. From how many metals, the electrons will be ejected if their surfaces are irradiated with an electromagnetic radiation of wavelength 300 nm? (h = $6.6 \times 10^{-34}$ Js, 1 eV = $1.6 \times 10^{-19}$ J)