Arrange the following elements in order of increasing first ionization enthalpy: B, C, N, O.
First ionization enthalpy generally increases across period 2, but N (half-filled 2p³) has higher stability than O. Order: B < C < O < N.
Ref: NCERT Class 11 Chemistry > Chapter 3: Classification of Elements and Periodicity in Properties > Topic: Periodic Trends - Atomic Radii Ionic Radii and Ionization Enthalpy
