The first ionization enthalpies of C , N and F are 1086 , 1402 and 1681 kJ mol ⁻¹ respectively. The first ionization enthalpy ( kJ mol ⁻¹ ) of O is most likely to be:

Step-by-step solution

In the second period, the general trend is an increase in first ionization enthalpy from left to right. However, Nitrogen ( Group 15 ) has a stable half-filled 2 p ^3 electronic configuration, making its first ionization enthalpy higher than that of Oxygen ( Group 16 ). The correct order of first ionization enthalpies is C Therefore, the first ionization enthalpy of O must lie strictly between that of C ( 1086 kJ mol ⁻¹ ) and N ( 1402 kJ mol ⁻¹ ). Among the given options, only 1314 kJ mol ⁻¹ falls in this range. An