Question

In which of the following pairs of ions, the lower oxidation state in aqueous solution is more stable than the other?

• A. $T{i}^{+}$, $T{i}^{3+}$
• B. $C{u}^{+}$, $C{u}^{2+}$
• C. $C{r}^{+}$, $C{r}^{3+}$
• D. None of these

Answer 1

The correct option is A $T{i}^{+}$, $T{i}^{3+}$

The electronic configurations are:

$T{i}^{+}-\left[Ar\right]3d^{1}4s^1$ ; $T{i}^{3+}-\left[Ar\right]3d^{1}4s^0$

$C{u}^{+}-\left[Ar\right]3d^{10}4s^0;C{u}^{2+}-\left[Ar\right]3d^{9}4s^0$

$C{r}^{+}-\left[Ar\right]3d^{5}4s^{0}C{r}^{3+}-\left[Ar\right]3d^{3}4s^0$

In solutions, hydration enthalpy of ions also affect their stability.

So, based upon both fact i.e electronic configuration and hydration enthalpy $T{i}^{+}$ is more stable than $T{i}^{3+}$ in solution while in other two cases higher oxidation state ions are more stable.