Neptunium (Z = 93, $[\mathrm{Rn}]5f^{4}6d^{1}7s^2$) reaches the highest oxidation state shown by actinoids. The oxidation state and the number of $5f$ electrons left on the metal ion in that state are respectively

1. A$+7$ and $0$
2. B$+7$ and $4$
3. C$+5$ and $2$
4. D$+6$ and $1$