What is Variable Valency ? Name two elements having variable valency and state their valencies.

Hint: An element's valency is its ability to combine with other elements. The valency of an element is the amount of electrons supplied or received by an atom in order for it to have the electronic configuration of the closest noble gas. The combining power of an element is known as valency. The valency of elements in the same group of the periodic table is the same. The number of electrons in an element's outer shell determines its valency.

Complete answer:
The valency of the same element might fluctuate due to different conditions under which a chemical reaction takes place. As a result, metals such as lead, tin, copper, mercury, iron, and others have varying valency. Metals donate electrons from their valence shell to produce positively charged ions in most cases. Some metals, on the other hand, lose electrons from the shell next to the valence shell. The element has more than one electropositive valency in this circumstance. Variable valency is a term used to describe such components. The number of electrons lost or acquired by an element's atom during the creation of ionic bonds is its electrovalency.
Variable valency is not displayed in the s-block elements. P-block elements with higher atomic numbers and inner transition elements, on the other hand, have variable valency.
There are two primary reasons why variable valency is seen.
1. The impact of inert pairs in p-block elements.
2. In transition elements, there is a small energy difference between $ns$ and $(n-1)d$ sub shells, and $ns$ and $(n-2)$ subshells in inner transition elements.
Examples
Iron $F{e^{2 + }},F{e^{3 + }}$
Copper $C{u^{2 + }},C{u^{3 + }}$.

Note:
Valence electrons are electrons that are present in an atom's outermost shell. As a result, one or more electrons from the core's outermost shell may be lost when valence electrons are removed. As a result, such items have variable valence, indicating that they have two or more different valencies. Depending on the nature of the reaction, some elements combine with other atoms to provide, take, or exchange electrons in varying amounts. For starters, both ferrous and ferric oxide are formed when iron reacts with oxygen. It's known as the valence element.