Answer:
The correct option is: C. Ca, Mg, Be
Explanation:
First ionization energy of a chemical element refers to the energy needed to completely remove one valence electron from the outermost electron shell or valence shell of a gaseous atom.
The ionization energy decreases down the group and increases across a period. Elements having stable half-filled or fully-filled electron configuration have high ionization energy. Also, elements having high electronegativity have higher ionization energy.
Thus the ionization energy of the second group elements i.e. alkaline earth metals, decreases as we go down the group from beryllium to calcium.
Therefore, the increasing order of first ionization energy is correct in this set: C. Ca, Mg, Be.
