Question

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

Answer 1

Hint: Ionization energy is the amount of energy needed to remove an electron from its neutral atom. Ionization energy decreases while moving from top to bottom, and increases while moving from left to right in the periodic table. Thus, alkali metals have low ionization energy.

Complete answer:
Chemical elements are the purest form of atoms. There are a total of $118$ elements arranged in the increasing atomic numbers in vertical columns and horizontal rows. Vertical columns were known as groups, and horizontal rows were known as periods. There are a total of $7$ periods and $18$ groups in the periodic table.
As the electron is added to an extra shell in groups, the nuclear attraction on valence electrons decreases resulting in low ionization energy. Whereas in periods the electron is added to the same shell, the nuclear attraction on valence electrons increases results in higher ionization energy.
Francium is the element with atomic number $87$ has one electron in its valence shell belonging to alkali earth metal. As it is the element with more shells, it has low ionization energy.
Thus, francium is an element in the periodic table that has the smallest ionization energy.

Note:
The elements that belong to group $1$ are alkali earth metals. These all elements have only one electron in its valence shell. The removal of one electron from its valence shell in alkali earth metals is easy. Thus, alkali earth metals have low ionization energy in the periodic table.