Arrange Be, Ca, Ba, Ra in increasing order of ionization energy:
a.) Be < Ra < Ca < Ba
b.) Ba < Ca < Ra < Be
c.) Ra < Ba < Ca < Be
d.) Ba < Ra < Ca < Be

Hint: The amount of energy required to remove the outermost valence electron from an atom or an ion in its ground state is called ionization energy.

Complete step by step answer:
In the question it is given that, arrange the given elements in increasing order of ionization energy.
The given elements are Beryllium (Be), Calcium (Ca), Barium (Ba), and Radium (Ra).
All the given elements belong to II A group nothing but s-block elements.
The atomic numbers of given elements is as follows.
Atomic number of Beryllium - 4
Atomic number of Calcium - 20
Atomic number of Barium - 56
Atomic number of Radium – 88
From the atomic numbers we can easily say that Beryllium is the starting element in II A group and Radium is the last element in II A group.
We know that as we are moving from top to bottom in the periodic table the atomic size of the atoms increases.
So, the increasing order of ionization energy of given elements is as follows.
Ra < Ba < Ca < Be
So, the correct answer is “Option C”.

Note: As the atomic size increases the ionization energy decreases due to less attraction of valence electrons by the nucleus of the atom. Because a lot of electrons are going to add to the new orbitals as we are moving from top to bottom in the periodic table.