What is the lightest element out of the following options?

Lithium (Li), Magnesium (Mg), Scandium (Sc), Florine (F), Aluminum (AI), Phosphorus (P), Nitrogen (N), Chlorine (CI), Silicon (Si), Carbon (C), Argon (Ar), Neon (Ne), Helium (He), Beryllium (Be), Oxygen (O), Sulfur (S), Calcium (Ca), Sodium (Na).