Which element has the configuration [Kr] 5s² 4d⁷?

The electron configuration [Kr] 5s² 4d⁷ corresponds to the element Rhodium (Rh) because it indicates that the element has a total of 45 electrons, which is characteristic of Rhodium. The configuration can be broken down as follows:

• [Kr] accounts for the 36 electrons of Krypton, the preceding noble gas, emphasizing that Rh is heavier and further down the periodic table.

• The 5s² indicates that there are 2 electrons in the 5s subshell.

• The 4d⁷ specifies that there are 7 electrons in the 4d subshell.

When you add those together (36 from [Kr] + 2 from 5s² + 7 from 4d⁷), you arrive at 45, which matches the atomic number for Rhodium. This systematic building up of the electron configuration through subshell filling follows the aufbau principle, where electrons fill the lowest energy orbitals first.

The other elements provided do not have this specific electron configuration. Ruthenium (Ru), for instance, would have a configuration of [Kr] 5s² 4d⁵, Palladium (Pd) has an atypical configuration