Solution

Actinoids are element 89 to 103 and fill their $$5 \mathrm{f}$$ shell. They are typical metals and radioactive also. $$E g-T h, U, P u$$.



$$U(z=92) \rightarrow 5 f^{3} 6 d^{1} 7 s^{2}$$

$$N{p}(z=93) \rightarrow 5 f^{4} 6 d^{1} 7 s^{2}$$

$$P u(z=94) \rightarrow 5 f^{6} 6 d^{0} 7 s^{2}$$

$$A m(z=95) \rightarrow 5 f^{7} 6 d^{\circ} 7 s^{2}$$



So, U and $$Np$$ have one electron in $$6 d$$ orbital.