For a first-row transition metal, the expected ground-state electron configuration with the most unpaired electrons is 3d^5. This configuration corresponds to the metal ion with the highest oxidation state, which is typically +5. The 3d^5 configuration has five unpaired electrons, which gives rise to the maximum possible paramagnetism. The electron configuration can be represented as:

$$(1s)^2(2s)^2(2p)^6(3s)^2(3p)^6(3d)^5$$

An example of a first-row transition metal that exhibits the 3d^5 configuration is manganese (Mn). In its +5 oxidation state, manganese has the electron configuration 1s^22s^22p^63s^23p^63d^5. This configuration results in five unpaired electrons in the 3d orbitals, making Mn5+ one of the most paramagnetic ions among the first-row transition metals.