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

The electron configuration [Kr] 5s² 4d² corresponds to the element that has a total of 40 electrons. The notation [Kr] indicates that the first 36 electrons are arranged in the noble gas configuration of krypton. The next two electrons fill the 5s subshell, and the following two fill the 4d subshell.

When counting the total number of electrons, the configuration shows that there are 36 from krypton, 2 from the 5s subshell, and 2 from the 4d subshell, summing to a total of 40 electrons. The element with an atomic number of 40 is zirconium (Zr), which aligns perfectly with this electron configuration.

The other elements listed, gallium, yttrium, and germanium, have different atomic numbers and therefore different electron configurations. Gallium has an atomic number of 31, yttrium is 39, and germanium is 32. None of these elements can match the electron configuration given in the question, confirming that zirconium is the only correct answer.