In which case effective nuclear charge is minimum?

Effective nuclear charge,Zeff=Z−Swhere, Z- atomic number and S = screening constant= 0.35 per electron for electron in nth orbit.= 0.85 per electron for electrons in (n - 1)th orbit= 1.00 per electron for electrons in (n - 2)th, (n - 3)th, (n - 4)th orbit= 0.30 per electron in Ls-orbital (when alone)Be, Ls2 2s2 one valence electron in 2s is screened by one electron in 2s-orbital (nth orbit) and two electrons in 1s orbital ((n - 1)th orbit.)∴S=0.35+2×0.85=2.05∴Zeff =4−2.05=1.95             (given)Be+ 1s2 2s1electron is screened by two electrons in 1 s-orbital ((n - 1)th orbital) S=2×0.85=1.70Zeff =4−1.70=2.30Be2+, 1s2 one s-electron in ls-orbital (alone exists) is screened by another electron in same orbit. Thus,S=0.30Zeff =4−0.30=3.70Be3+,1s1no screening (single electron)Thus, Zeff =4. Thus, Zeff :Be