Calculate the energy required for the process He+(g) → He2+(g) + e−. The ionization energy for the H atom in the ground state is 2.18 × 10⁻¹⁸ J/atom.

Given that,
The I.E for H atom is 2π²me⁴/h² = 2.18 × 10⁻¹⁸ J/atom.
For He+, Z² = 2² = 4
For the given process, the energy required = Z² × 2π²me⁴/h² = 4 × 2π²me⁴/h² = 4 × 2.18 × 10⁻¹⁸ = 8.72 × 10⁻¹⁸ J/ion.