The second ionisation enthalpies of elements are always higher than their first ionisation enthalpies because:

Options

A. cation formed always have stable half filled or completely filled valence shell electron configuration.
B. it is easier to remove electron from cation.
C. ionization is an endothermic process.
D. the cation is smaller than its parent atom

Answer

D

Explanation

As elements are ionized, the proton to electron ratio increases, so the attraction between valence shell electron and nucleus increases and as a result the size decreases. Therefore, the removal of electron from smaller cation requires higher energy. Hence the second ionisation enthalpy is greater than its first ionisation enthalpy.