Ionisation energy of an element is the amount of energy needed to remove one electron from each atoms of an element in the gaseous state.
When an atom loses an electron it becomes positively charged ion.
X(g) → X+(g) + e-
The energy needed to remove 2nd electron from each ion in a mole of gaseous ion is the second ionisation energy.
X+(g) → X2+(g) + e-
Factors that increase…