Which element corresponds to the electron configuration [Kr] 5s^2 4d^3?

The electron configuration [Kr] 5s^2 4d^3 indicates that the element in question has a total of 43 electrons when considering the 36 electrons from krypton (Kr) along with the additional electrons in the outer shells: 2 from the 5s subshell and 3 from the 4d subshell. Adding these together gives us 36 + 2 + 3 = 41 electrons.

The element with 41 electrons is niobium (Nb), which is located in group 5 of the periodic table. The configuration reflects that niobium has its outermost electrons filling the 5s and 4d subshells.

Ruthenium, silver, and palladium have different electron configurations, which do not match this specific arrangement. Therefore, the correct identification of the element based on the given electron configuration is indeed niobium (Nb).