Final answer:
The elements with the lowest ionization energy are located in the lower left corner of the periodic table, particularly in the far-left columns. Rubidium (Rb) has one of the lowest first ionization energies according to the trends of increasing ionization energy from left to right and from bottom to top.
Step-by-step explanation:
The elements with the lowest ionization energy can be found in the lower left corner of the periodic table. Ionization energy tends to increase as you go from left to right in a period and from bottom to top in a group. This means that the alkali metals, which are found in the far-left columns of the periodic table, generally have the lowest first ionization energies. Specifically, Rubidium (Rb), which is located towards the bottom of the first column, has one of the lowest ionization energies.
Utilizing the periodic table trends, elements in the two far-left columns form a rectangle, and the element at the bottom left of this rectangle—Rubidium (Rb)—has the lowest first ionization energy amongst them. This is because the atomic size increases and nuclear charge has a lesser effect on the outermost electron as you move down a group, making it easier to remove an electron and thus resulting in lower ionization energy.