The `+1` oxidation state is more stable than the +3 oxidation state for thallium. Explain why ?

Explanation

The outer electronic configuration of thalium 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 attracted by the nucleus than `6p^(1)` electron. Therefore, `6s^(2)` electrons do not participate in bond formation. Instead only `6p^(1)` electron takes part is more stable than its `+3` state.