The `+1` oxidation state is more stable than `+3` oxidation state for thallium. Give reason.

Answer

The outer electronic configuration of thallium is `6s^(2),6p^(1)`.Therefore, it can show oxidation states of `+1` and `+3` But due to inert pair effect, the `6s^(2)` electrons are more strongly attaracted by the nucleus than `6p^(1)` electron.Therefore, `6s^(2)` electrons do not participate in bond formation.Instead only `6p^(1)` electron takes part in bond formation and hence thallium shows an oxidation state of `+1`.Thus, `+1` oxidation state of thallium is more stable than its `+3` state.