Final answer:
In a polyelectronic atom, the 3d sublevel typically has the highest energy level when compared to the 4s, 2p, and 3s sublevels.
Step-by-step explanation:
In answering the question of which electronic configuration in a polyelectronic atom has the highest energy level, we must refer to the principles of electronic structure and atomic orbitals. According to the Aufbau principle, electrons fill atomic orbitals of the lowest available energy levels before occupying higher levels. However, due to the energies of sublevels in different principal energy levels overlapping, the energy order is not strictly based on the principal quantum number, n.
Based on observed experimental results and theoretical calculations, after the 3p sublevel, the 4s is actually lower in energy than the 3d, but upon moving past the 3d level, the energy starts to increase. Therefore, of the given options (a) 4s, (b) 3d, (c) 2p, and (d) 3s, the 3d sublevel typically has the highest energy level compared to 4s, 3s, and 2p sublevels in polyelectronic atoms.