Which element matches the electron configuration [Kr] 5s^2 4d^2?

The electron configuration [Kr] 5s² 4d² indicates that the element in question has a total of 40 electrons (since krypton has 36 electrons, adding 2 from the 5s subshell and 2 from the 4d subshell).

To determine which element corresponds to this electron configuration, it's essential to follow the order of filling electron orbitals. After the noble gas configuration of krypton ([Kr]), the next electrons fill into the 5s orbital first, followed by the 4d orbitals. The notation 5s² indicates two electrons in the 5s orbital, and the notation 4d² signifies two electrons in the 4d orbitals.

When counting from the first element (hydrogen) to the element matching this configuration, the 40th element on the periodic table is zirconium (Zr), which has the atomic number 40. Its electron configuration exactly matches [Kr] 5s² 4d², confirming that it is the element in question.

Understanding the correct filling order of electrons based on energy levels and sublevels is key to associating an electron configuration with the correct element.