Question

how can we know the period number​

Answer 1

Here we find that the no of valence electrons of element is 7 as the valence shell has 7 electrons. ... Now to find the period we have to understand that the period is the number of shell the element is having therefore here chlorine has 3 shells (K-2, L-8, and M-7). So the period of the given element is 3.

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