Variable valency

Hy!

Steemit friends!

I am going to describe the topic variable valency.
Since valency is the combining power of atom of an element with other element.Some element have fixed valency such that
The valency hydrogen is 01
The valency of carbon is 04
The valency of sodiam is 01 and chlorine is also 01.But some elements show more than one valency.
If an element show more than one valency in different compounds then their valency is called variable valency. e.g
The valency of iron is 2 in ferrous compound
While 3vin ferric compounds
Similarly the valency of copper is 2,3

Thanks...