Question

How to take out valency?

Answer 1

The first(and easiest) is simply to consult the periodic table. The elements are sorted into groups, and the elements in the groups(1–8 respectively) have the same valency as others in their group. For example, all of the elements in group 8 have eight electrons(high stability).

Answer 2

Firstly,know the atomic no. of the element you want to find valency.then
subtract in the order 2,8,8....
ex :- Na (atomic no.= 11)= 2,8,1....and the last no. is 1 .so its valency is 1.