Valency - it is the combining capacity if an atom.
Fem 1 - 4 the valency remains the same.
N frm 5...subtract it with 8.
Like for example..
atomic no: of carbon is 6
So it's electronic configuration will be 2 ,4.
Therefore it's valency = 4
Anthr example - the atomic numbr of nitrogen is 7.
Therefore it's E.C will be - 2,5
Valency = 8-5=3
Hope it helped