Question

In which of the following $+1$ oxidation state is more stable than $+3$?

• A. $Ga$
• B. $In$
• C. $TI$
• D. $Al$

Answer 1

The correct option is C $TI$

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 answer is option (C).