According to I.C slater effective nuclear charge, `Z^(**)`, due to screening, is not exactly equal to the actual nuclear charge Z of the nucleus of the atom. `Z^(**)` depends on the type of orbitals in which the electron is housed, and on the ability of other electrons in more penetrating orbitals to screen the electron in question from the nucleus. The relative extent to which the various orbitals penetrate the electron clouds of other orbitals is `s gt p gt f` . The effective nuclear charge `Z^(**)` due to screening is given by `Z^(**)=Z-sigma`, where Z is the atomic atomic number and `sigma` is the slater screening constant values `0 lt sigma lt Z` Screening effect of one electron in the outermost orbitals, is not considered in calculate of `sigma`. In which of the following cases the concept of `Z^(**)` is applicable?A. Ionisation energy increases as `Z^(**)` increasesB. Electronegativity of the atom increases as `Z^(**)` increasesC. The ionisation energy of `Na, K^(-), Rb^(-)` , are comparable because of equal `Z^(**)`D. All of the above