Which of the following elements has the configuration [He] 2s^2 2p^5?

The electron configuration [He] 2s² 2p⁵ represents an element with a total of 17 electrons when you account for the helium core (2 electrons) and the additional electrons in the 2s and 2p orbitals. First, the 2s² indicates that 2 electrons occupy the 2s subshell, while 2p⁵ indicates that there are 5 electrons in the 2p subshell.

When you combine the electrons from the 1s (2 from helium) and the given configuration, you sum them to get 2 + 2 + 5 = 17 electrons. The atomic number, which corresponds to the number of protons in the nucleus of the atom, is also 17, identifying the element as chlorine. However, since the answer options only include lighter elements, we must identify the closest configuration.

The element represented by the configuration [He] 2s² 2p⁵ is fluorine, with an atomic number of 9. It has 7 valence electrons (2s² 2p⁵), which respectively belong to the second energy level. Fluorine needs one additional electron to fill its p subshell,