Question

How to find the valency of an element?

Answer 1

For non-metal 
    ⇒ 8 - number of electrons in the outermost (valence) shell of atom.

for example, valency of sulphur ( a non-metal)
sulphur have six electrons in the outermost shell of atom  
 ⇒ 8 - 6 = 2 is the valency of sulphur

For metal
 ⇒ number of electrons in the outermost (valence) shell of atom.

for example, valency of aluminium ( a metal )
aluminium has 3 electrons in the outermost shell of atom
⇒ 3 is the valency of aluminium