Answer:
c) Cu⁺(g)⟶ Cu²⁺(g) + e⁻
Step-by-step explanation:
Ionization energy is the energy needed to remove a valence electron from a gaseous atom.
b) Cu(g) ⟶ Cu⁺(g) + e⁻ represents the first ionization energy, the energy needed to remove the first electron.
c) Cu⁺(g)⟶ Cu²⁺(g) + e⁻ represents the second ionization energy of Cu, the energy needed to remove the second electron after the first one is gone.
a) is wrong. The charge is not balanced.
d) is wrong. It represents the electron gain energy of a Cu⁻ ion (highly unlikely).
e) is wrong. It represents the electron gain energy of a Cu⁺ ion (the reverse of the first ionization energy).