Question

The element that forms stable compounds in low oxidation state is:

• A. $Mg$
• B. $Al$
• C. $Ga$
• D. $Tl$

Answer 1

The correct option is D $Tl$

The element that forms stable compounds in low oxidation state is $Tl$. The two electrons in the outer shell tend to remain paired and do not participate in compound formation (inert pair effect).

Due to this, $Tl\left(I\right)$ compounds are more stable than $Tl\left(III\right)$ compounds.

$Tl\left(III\right)$ ions act as oxidising agents and changes to $Tl\left(I\right)$ ions.

$T{l}^{3+}+2e^{-}\to T{l}^{+}$

Hence, option $D$ is correct.