Question

Which element in the periodic table has the smallest ionization energy ?

Answer 1

Answer
Ionization energy increases across a Period (left to right) and decreases down a Group (top to bottom).
Explanation :
Given the above, the element with the lowest ionization energy should be a heavy alkali metal, maybe francium, $Z=87$. As a chemist, as a physical scientist, you should look up tables of ionization energies on the interwebz, and see if this hypothesis is confirmed. Here is a leading link You may find a better site.