In which of the following pairs,

$\mathrm{Fe}^{2+}$ and $\mathrm{Co}^{+}$

$\mathrm{Cr}^{+}$and $\mathrm{Mn}^{2+}$

$\mathrm{Ni}^{2+}$ and $\mathrm{Cu}^{+}$

$\mathrm{V}^{2+}$ and $\mathrm{Cr}^{+}$