Question

how are the elements having variable valency named

Answer 1

The combining power or the combining capacity of an atom or an element is called its valency. Valency of an element is decided by number of outermost shell electrons. If an element exhibit more than one valency . This is known as variable valency. 

For example

1) Iron (Fe) can show a valency of 2 and 3

2) Copper (Cu) can show a valency of 1 and 2

3) Phosphorus can show a valency of 3 and 5