Question

how are the elements with variable valency named?

Answer 1

Valency is defined as the combining capacity of an element. For example, the valency of Hydrogen is 1 as it has one electron in its outermost shell and requires one electron to become stable.

Some elements differ in their capacity to combine with other elements depending on the nature of the reaction; this property is called variable valency. For example, Iron (Fe) can have a valency of both 4 and 3.

Fe 3+ Ferrate
Fe 2+ Ferrous

Answer 2

on the basis of atomic number and product!
hope it will help you out!