inert pair effect
Kindly refer to the following links:
https://www.meritnation.com/ask-answer/question/plz-explain-inert-pair-effect/the-s-block-elements/1773198
https://www.meritnation.com/ask-answer/question/what-is-the-inert-pair-effect/the-p-block-elements/1755530
https://www.meritnation.com/ask-answer/question/what-is-inert-pair-effect-explain-in-detail-with-examples/chemical-bonding-and-molecular-structure/3693183
https://www.meritnation.com/ask-answer/question/plz-explain-inert-pair-effect/the-s-block-elements/1773198
https://www.meritnation.com/ask-answer/question/what-is-the-inert-pair-effect/the-p-block-elements/1755530
https://www.meritnation.com/ask-answer/question/what-is-inert-pair-effect-explain-in-detail-with-examples/chemical-bonding-and-molecular-structure/3693183