" The stability of "+1" oxidation state increases in sequence "

The stability of +1 oxidation state increases in the sequence

Stability of + 1 oxidation state increases in the sequence-

The stability of +1 oxidation state increases in the sequence :

The stability of +1 oxidation state increases in the sequence :

Due to inert pair effect, the stability of +2 oxidation state increases on moving down the group 14. Why?

Explain the following : The stability of + 5 oxidation state decreases down group 15.