Answer
See explanation
Work Step by Step
The work function is the energy required to remove an electron from an atom on the surface of a metal. It differs from the ionization energy, which is the energy required to remove an electron from a gaseous atom.
In the context of metals, the electrons in the outermost shell (valence electrons) experience a weaker effective nuclear charge due to shielding effects from inner electrons. Therefore, the energy required to remove these valence electrons is lower than the energy required to remove an electron from a gaseous atom of the same element.
Ionization energy: $M(g)\rightarrow M^+(g)+e^-$
Work function:
$M(s)\rightarrow M^+(s)+e^-$
