What is Inert Pair Effect ?

 What is Inert Pair Effect ? 

This effect is applicable only from group 13th to 15th

In P-block elements when we move down the group from 5th to 6th period elements, there exists 14 Lanthanoid elements in which last electron enters in f-subshell due to poor shielding provided by f-subshell the Effective nuclear charge increases and apply more attraction on ns electrons, As a result of which the tendancy of ns electrons to participate in bonding decreases this effect called Inert Pair Effect. 

B →+3(Oxidation State)

Al 

Ga 

In 

Tl →+1(Oxidation State) 

Due to Inert Pair Effect, Oxidation State decreases by 2units.

Higher elements show higher oxidation state

Lower elements show lover oxidation state.