The ionization energy of a hydrogen atom from its ground state is 2.18 × 10⁻¹⁸ J. What is the energy required to ionize
For He⁺ (Z=2), E = 4 × 2.18×10⁻¹⁸ = 8.72×10⁻¹⁸ J.
Ref: NCERT Class 11 Chemistry > Chapter 2: Structure of Atom > Topic: Quantum Numbers - Principal Azimuthal Magnetic Spin