Question

What is the meaning of Valency of group remain same as number of electrons in the outermost shell remains same

Answer 1

As we move down a group, the number of valence electrons remains the same, even though the number of shells increases. While valence electrons across a period incrementally climb by one, the number of shells remaining the same. The period number (row number, to remind you) in which an element can be found indicates the number of shells encircling its nucleus.
While the period number indicates the number of shells, the group number indicates the number of valence electrons in the outermost shell.Specifically, the number in the ones’ place. However, this is only true for the main group elements – the elements inhabiting groups 1-2 and 13-18.