Which element in the fourth period has the highest third ionization enthalpy?
Third ionization enthalpy peaks when removing an electron from a noble gas-like X²⁺ ion. Ca (after losing two electrons, becomes Ca²⁺ with 1s² 2s² 2p⁶ 3s² 3p⁶) has the highest value.
Ref: NCERT Class 11 Chemistry > Chapter 3: Classification of Elements and Periodicity in Properties > Topic: Periodic Trends - Atomic Radii Ionic Radii and Ionization Enthalpy