What element in period 4 has the lowest ionization energy? noble gas, alkali metal, halogen or alkaline earth metal?

alkali metal

Explanation:

The alkali metals in period 4 will have the lowest ionization energy of the elements in the period.

Across a period ionization energy increases progressively from left to right due to decreasing atomic radii caused by the increasing nuclear charge which is not compensated for by successive electronic shells.

Down a group, it decreases.

c. 4.54 x 10–12 j happens to be correct