Question

what is the difference between valence electron and valency

Answer 1

valence electrons re the electrons present in the outermost shell.
whereas valency specifies the ability of atom to attain octat state
for eg,valency of electron is 6.
but the valency is 2. this is because it needs two more electrons to attain octat state.

Answer 2

LISTEN THERE ARE DIFFERENT ELECTRONIC CONFIGURATIONS OF DIFFERENT ELEMENTS.
FOR EX - IF ELECTRONIC CONFIGURATION OF AN ELEMENT IS 2,8,8.
THEN THE NO. OF ELECTRONS IN LAST SHELL ARE VALENCE ELECTRON.

AND IF THE VALENCY WOULD BE 2,8,6 THEN THE NO. OF ELECTRONS REQUIRED TO COMPLETE OCTATE IS VALENCY