Question

The correct increasing order of the stability of $A{l}^{+},G{a}^{+},I{n}^{+},T{l}^{+}$ ions are:

• A. $A{l}^{+}<G{a}^{+}<T{l}^{+}<I{n}^{+}$
• B. $A{l}^{+}<G{a}^{+}<I{n}^{+}<T{l}^{+}$
• C. $T{l}^{+}<I{n}^{+}<G{a}^{+}<A{l}^{+}$
• D. $T{l}^{+}<A{l}^{+}<G{a}^{+}<I{n}^{+}$

Answer 1

Answer: (B)

$A{l}^{+}<G{a}^{+}<I{n}^{+}<T{l}^{+}$

The inert pair effect is the tendency of the electrons in the outermost atomic S orbital to remain unionized or unshared in compounds of post-transition metals. The term inert pair effect is often used in relation to the increasing stability of oxidation states that are two less than the group valency for the heavier elements of groups 13, 14, 15 and 16.
As an example in group 13 the +1 oxidation state of $Tl$ is the most stable and $T{l}^{3+}$ compounds are comparatively rare. The stability of the +1 oxidation state increases in the following sequence:
$A{l}^{+}<G{a}^{+}<I{n}^{+}<T{l}^{+}$