Question

Thallium shows different oxidation states because

Answer 1

Thallium shows +1 and +3 oxidation state because of inert pair effect Inert pair effect is a term often used to describe valence electrons in an s orbital penetrating to the nucleus better than electrons in p orbitals making them more tightly bound to the nucleus due to poor shielding effect offered by the inner sub-shells/orbitals and causing bonds involving these electrons to become unfavorable due to the large promotion energy involved.