Question

what are the causes of variable valency​?

Answer 1

Answer:

The electrons which are present in an atom's outermost shell are called valence electrons.

The electrons present in the outermost shell of an atom are called valence electrons.

If the valency electrons are removed, the remainder is called Core.

In case of transition elements, the core is not stable.

So after the removal of valency electrons, one or more electrons can be lost from the outermost shell of the core also.

Hence these elements show two or more different valencies i.e. they have variable valency.

Example: Iron has two valencies  2+ and 3+

Answer 2

Answer:

Refers to the attachment.

Explanation:

Some elements show variable valency because of the different electronic configurations. An atom of an element can sometimes lose more electrons than are present in its valence shell i.e. loss from the penultimate shell and hence exhibit more than 1 or variable valency.