Periodic Table

The correct option (D): Negligible screening effect of 'f' orbitals.

The correct option (B): .

To determine which electronic configurations belong to main group elements, we need to examine the positions of these elements in the periodic table. Main group elements are those found in the s- and p-blocks.
- A. [Ne]3s : This configuration corresponds to an element in the alkali metal group (main group element).
Thus, A is correct.
- B. [Ar]3d 4s : This configuration corresponds to an element in the d-block (transition metal), not a main group element.
Thus, B is incorrect.
- C. [Kr]4d 3s 5p : This configuration corresponds to an element in the p-block (halogen).
Thus, C is correct.
- D. [Ar]3d 4s : This configuration corresponds to an element in the d-block (transition metal), but it involves the 4s orbital, which is characteristic of main group elements.
Thus, D is correct.
- E. [Rn]5f 6d 7s : This configuration corresponds to an element in the f-block (lanthanide series), not a main group element.
Thus, E is incorrect.

Thus, the correct answer is (3) A, C, and D only.