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

The electron configuration [Kr] 5s^2 represents an element that has the noble gas krypton as its core configuration, followed by two electrons in the 5s subshell. To determine the element corresponding to this configuration, it’s essential to recognize that the notation indicates the total number of electrons in the atom, which is determined by adding the electrons from krypton and the additional electrons in the 5s subshell.

Krypton (Kr) has an atomic number of 36, meaning it has 36 electrons. The 5s^2 notation indicates that there are two additional electrons in the 5s subshell. Therefore, the total number of electrons in the atom is 36 (from Kr) + 2 (from 5s^2), which equals 38. The element with an atomic number of 38 is strontium (Sr).

This matches perfectly with the given electron configuration, affirming that strontium is the correct answer. The other elements listed do not have the same number of electrons and therefore have different electron configurations. Rubidium has an atomic number of 37, yttrium has 39, and zirconium has 40, none of which fit the [Kr]