The element is most likely PHOSPHORUS.
Phosphorus is an element with an atomic number of 15. The electronic configuration of the element is 2,8,5. This configuration implies that, each atom of phosphorus has three sub shell, the first sub shell has 2 electrons, the second has 8 electrons while the outermost sub shell has 5 electrons. The electrons in the outermost shell are also called the valence shell. Thus, phosphorus has 5 electrons in its valence shell.