Question

Which one of the follwing is stable oxidation state of Tl?

• A. 1
• B. 3
• C. 2
• D. (b) and (c) above.

Answer 1

The correct option is A 1

In Ga, In and Tl, both +1 and +3 oxidations states are observed but +1 oxidations state of Tl is relative more stable.
The stability of +1 oxidation state among Al, Ga, In and Tl increases in the sequence Al<Ga<In<Tl.
This is due to inert pair effect due to which, on moving down the group, the stability of +3 oxidation state decreases while the stability of +1 oxidation state increases.
Hence correct option is a.