The cause of periodicity in properties of the elements is the repetition of__________after certain regular intervals.

Options

A. similar penultimate shell electronic configuration
B. similar antepenultimate shell electronic configuration
C. similar outermost shell electronic configuration
D. similar valence shell electronic configurations

Answer

D

Explanation

The properties of the elements are repeated after certain regular intervals because with a gradual increase in atomic number, there occurs a repetition of similar valence electronic configurations. For example, all the elements of group `1(1A)` have `ns^(1)` valence shell outmost shell. similarly, all the halogens and noble hases (except `He)` have `ns^(2)np^(5)` and `ns^(2)np^(6)` valence shell electronic configuration, respectively.