Question

how to identify metal surface used in the photoelectric effect apparatus by work function of a metal

Answer 1

When the photons from the light strike the metal they deliver an amount of energy which depends on the frequency of the light. If the energy delivered is greater than the binding energy of the outermost electron in the metal, it is emitted. These binding energies - electron-volts, eV - (="work functions") are different ofr different metals. (Table of some ... http://hyperphysics.phy-astr.gsu.edu/hbase/tables/photoelec.html)