Atomic numbers: U 92, Np 93, Pu 94, Am 95, with ground-state configurations $5f^{3}6d^{1}7s^2$, $5f^{4}6d^{1}7s^2$, $5f^{6}7s^2$ and $5f^{7}7s^2$ respectively. Among the tripositive ions of these four elements, the one with the largest spin-only magnetic moment is

1. A$\mathrm{Am}{}^{3+}$
2. B$\mathrm{Np}{}^{3+}$
3. C$\mathrm{U}{}^{3+}$
4. D$\mathrm{Pu}{}^{3+}$