Electron affinity (EA) is the energy change when an atom gains an electron: X + e⁻ → X⁻. The ionization potential (IP) is the energy to remove an electron: X → X⁺ + e⁻.

For the negative ion X⁻, its ionization potential is the energy for X⁻ → X + e⁻. This is the reverse of the electron affinity reaction for X. Therefore, the ionization potential of X⁻ is equal to the negative of the electron affinity of X.

Mathematically: $IP\left(X^{-}\right)=-EA\left(X\right)$

Final Answer: ionization potential of X⁻.