The properties of the elements (atomic/ionic radii, electron gain enthalpy, ionization enthalpy, electronegativity, valence, oxidising/reducing power, acid/base character, etc.) which are directly or indirectly related to their electronic configirations are called periodic properties. These properties show a regular gradation on moving from left to right in a period or form top to bottom in a group. Down a group, the atomic/ionic radii, metallic character and reducing character increase while ionization enthalpy and electronegativity decrease. Along a period from left to right, atomic/ionic and metallic character decrease while ionization enthaloy, electronegativity, non-metallic character and oxiding power increase. However, electron gain enthalpy becomes less negative down a group butmore negative along a period. In contrast, inert gases have positive electron gain enthalpies which do not show may regular trend.
Amomgst the following elements (whose electronic configurations are given below) the one having the highest ionization enthalpy is :
A. `[Ne] 3s^(2)3p^(1)`
B. `[Ne]3s^(2)3p^(3)`
C. `[Ne] 3s^(2)3p^(2)`
D. `[Ar] 3d^(10)4s^(2)4p^(3)`
