What is the inert pair effect?

To understand the inert pair effect, we need to understand the periodic table. There are some inherent properties of elements in the table. The inert pair effect is nothing but the extra stability concept. Generally p-block elements belonging to 3A, 4A, 5A, 6A, etc. show variable valency. For example, Sn element of group 4A shows +4 and +2 oxidation state. The higher oxidation state is called the group number oxidation state and +2 oxidation state is called the lower oxidation state which is equal to Group-2. Consider the configuration, if the electrons are lost from ns and np level, then group oxidation state of +4 is obtained while np electrons are only lost then +2 oxidation state is obtained due to its extra stability of ns electrons which are called inert pair. The effect is the inert pair effect.