What is the reaction that corresponds to the first ionization energy of rubidium

Rb (g) → Rb⁺ (g) + e⁻ I₁ = 1st ionization energy

Explanation:

Here we have

Rb (g) → Rb⁺ (g) + e⁻

The equation is of the form

X → X⁺ + e⁻

An atom that is made up of more than one electron requires a steadily increasing amount of energy to remove each successive electron. The ionization energy I₁ to remove the first electron is the first ionization energy, which can be defined as follows

E (g) → E⁺ (g) + e⁻ I₁ = 1st ionization energy

Similarly, the second ionization energy is given by

E⁺ (g) → E²⁺ (g) + e⁻ I₂ = 2nd ionization energy and so forth.