Q. Which of the following 3d-metal ion will give the lowest enthalpy of hydration ( $\left.\Delta_{\text {hyd }} H \right)$ when dissolved in water?
Solution:
Ion
$\Delta H _\text{ Hyd .}^{ \circ }( kJ / mole )$
$Cr^{2+}$
-1925
$Mn^{2+}$
-1862
$Fe^{2+}$
-1998
$Co^{2+}$
-2079
| Ion | $\Delta H _\text{ Hyd .}^{ \circ }( kJ / mole )$ |
|---|---|
| $Cr^{2+}$ | -1925 |
| $Mn^{2+}$ | -1862 |
| $Fe^{2+}$ | -1998 |
| $Co^{2+}$ | -2079 |