The ionisation energy `(IE_(1))` of an atom is defined as the energy needed to remove an electron from gaseous atom in its ground state. The 2nd ionisation energy `(IE_(2))` is the additional energy needed to remove the 2nd electron and so on. The successive ionisation energy of any species is increasing always.
In the graph below elements of period given with their ionisation energy. Select the one which represents an alkali metal:
A. X
B. Y
C. Z
D. L
