Answer: (a) Fluorine, F; (b) Hydrogen, H; (c) Helium, He
(a) Fluorine (F) is the most electronegative element: it is small and has a strong tendency to gain one electron.
(b) Hydrogen (H) has the smallest atomic mass (about 1 u).
(c) Helium (He) is the first noble gas, with only one shell, so it has the smallest atomic radius.