The energy required to remove both electrons from the helium atom in its ground state is 79.0 eV. How much energy is required to ionize helium (i.e., to remove one electron)?
(A) 24.6 eV (B) 39.5 eV (C) 51.8 eV (D) 54.4 eV (E) 65.4 eV
I can easily say that the answer will be (A) because single electron removing requires less than half the energy of removing both electrons. But if it is not multiple choice, I have to determine the answer by using an equation. What equation would I use to get this answer?