gives the most energy

Question

Which of the following reactions involves investing the most amount of energy?
A- (g) → A (g)
A (g) → A+ (g)
A+ (g) → A+2 (g)
A+2 (g) → A+3 (g)

Answer 1

A+2 (g) → A+3 (g) represents the third ionization energy which is greater than the first and second ionization energies.