Question

what is valency and how to calculate it

Answer 1

Valency is the no of electrons an element can donate
It is calculated as if a element is having atomic no. 12 that means it is having 2 electrons in its amoic radii so it can donate 2 electrons
And if 16 it can gain 2 electrons

Answer 2

valency is the thing which is needed by an element to octet configuration
valency of an element is taken by its valence electrons(outermost shell electrons)
ex:- the valency of oxygen is
atomic number=8
electronic configuration=2,6
valence electron=6
valency is 8-6=2
so the valency of oxygen is 2