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 valence-electron $Z^{\ast }$ values are evaluated for the third-period elements Na to Cl, each with the configuration $(1s{)}^2(2s,2p{)}^8(3s,3p{)}^k$. Which statements are correct?

1. AThe $Z^{\ast }$ of aluminium is smaller than that of magnesium.
2. BThe $Z^{\ast }$ of sulfur is 5.45.
3. CThe ratio $Z^{\ast }(\mathrm{Cl})/Z^{\ast }(\mathrm{Na})$ is 2.77.
4. D$Z^{\ast }$ increases by 0.65 for every unit increase in atomic number from Na to Cl.