Question

what is variable valency​

Answer 1

Answer:

Certain elements combine with other atoms, donating, accepting or sharing electrons in different proportions depending on the nature of the reaction. For example, iron combines with oxygen to form ferrous oxide as well as ferric oxide. This is termed variable valency. 

Answer 2

Answer:

Variable valency - definition

In transition elements, an atom loses electrons from the shell next to the valence shell (penultimate shell). In such a situation the element exhibits more than one valency (variable valency).