Use the following rule set. Slater's rules: write the configuration in groups $(1s)(2s,2p)(3s,3p)(3d)(4s,4p)(4d)(4f)(5s,5p)\dots$ For an electron in an $ns$ or $np$ group, every other electron in the same group contributes $0.35$ ($0.30$ for the $1s$ group), every electron in the $(n-1)$ shell contributes $0.85$, every electron in the $(n-2)$ or lower shells contributes $1.00$, and electrons in groups to the right contribute $0$. For an electron in an $nd$ or $nf$ group, every other electron in the same group contributes $0.35$, every electron in all groups to its left contributes $1.00$, and groups to the right contribute $0$. $Z^{\ast }=Z-S$. The $4s$ electrons of the $3d$-series atoms $\mathrm{Sc}$ to $\mathrm{Zn}$ (configuration $(3d{)}^x(4s{)}^2$) are considered. Which statements are correct?

1. A$Z^{\ast }(4s)$ of Sc is 3.00.
2. B$Z^{\ast }(4s)$ of Mn is the same as that of Sc.
3. C$Z^{\ast }(4s)$ rises by $0.15$ for each $3d$ electron added.
4. D$Z^{\ast }(4s)$ of Zn is 4.35.