What element is represented by the electron configuration [Kr] 5s^2 4d^4?

The electron configuration [Kr] 5s^2 4d^4 represents the distribution of electrons in an atom. In this configuration, the term [Kr] indicates that the atom has the same electron arrangement as Krypton, which accounts for the first 36 electrons. The additional 6 electrons specified by 5s^2 4d^4 bring the total to 42 electrons.

To break this down, the 5s^2 indicates that there are 2 electrons in the 5s subshell, and 4d^4 indicates that there are 4 electrons in the 4d subshell, making a total of 6 electrons beyond Krypton (36 + 6 = 42). The atomic number 42 corresponds to the element Molybdenum (Mo), confirming that it is the element represented by this electron configuration.

Understanding the order of filling of electron orbitals according to the Aufbau principle is crucial here. The 5s subshell is filled before the 4d subshell, leading to the correct arrangement. This orderly filling explains why Molybdenum, with 42 electrons, has this specific configuration.