The pair of lanthanoid ions which are diamagnetic is

Options

1. A$\mathrm{Ce}^{3+}$ and $\mathrm{Eu}^{2+}$
2. B$\mathrm{Gd}^{3+}$ and $\mathrm{Eu}^{3+}$
3. C$\mathrm{Pm}^{3+}$ and $\mathrm{Sm}^{3+}$
4. D$\mathrm{Ce}^{4+}$ and $\mathrm{Yb}^{2+}$