An element that has 3 valence electrons on its last shell and a total of 3 shells (energy levels) is aluminum (symbol: Al).
Aluminum has an atomic number of 13, which means it has 13 electrons. The electron configuration of aluminum is 1s² 2s² 2p⁶ 3s² 3p¹. In this configuration, the last shell (the third shell) contains 8 electrons, and the valence electrons are the three electrons in the 3p sublevel.