Answer
See answer below.
Work Step by Step
From the periodic table:
Also note that the question asks for one element, but any of the options listed is correct.
a) Period 2 nonmetal: C - Carbon, N - Nitrogen, O - Oxygen, F - Fluorine
b) Period 5 alkali metal: Rb - Rubidium
c) Period 3 halogen: Cl- Chlorine
d) Gas at 20°C and 1 atm: H - Hydrogen, He - Helium, N - Nitrogen, O - Oxygen, F - Fluorine,
$\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad$Ne - Neon, Cl - Chlorine, Ar - Argon, Kr - Krypton, Xe - Xenon, Rn - Radon
