Which of the following has the electron configuration [He] 2s^2?

The electron configuration [He] 2s^2 corresponds to an element that has a total of 4 electrons after accounting for the core electrons represented by the helium configuration. When we break down this configuration, [He] signifies that the first two electrons occupy the 1s orbital, which is the configuration for helium. The additional 2s^2 indicates that there are 2 electrons in the 2s subshell.

Now, if we look at the atomic number of beryllium, it is 4, which supports this configuration since it has exactly 4 electrons. The first two electrons fill the 1s orbital, and the next two fill the 2s orbital.

In contrast, carbon, neon, and fluorine have additional electrons leading to different configurations. Carbon, for instance, has 6 electrons, which would give it the configuration [He] 2s^2 2p^2. Neon, with 10 electrons, would have the configuration [Ne] 2s^2 2p^6. Fluorine has 9 electrons, translating to the configuration [He] 2s^2 2p^5.

Thus, beryllium is the