Is work function of a metal the same as ionisation energy?

Answer 1

In a simple answer ... NO, they are not the same.

Expanded answer ... The work function of a metal refers to the minimum energy required to release an electron from the surface of a metal by a photon of light. The ionization energy is the amount of energy required to remove an electron from an atom in the gaseous state. The work function is generally lower than the ionization energy for metals.