Question

which atmospheric gas is the lightest because it only has one proton and one electron and is made of only one element? ozone argon methane hydrogen

Explanation:

Hydrogen has one proton and one electron and is a single - element gas, making it the lightest among the options. Ozone is composed of oxygen atoms ($O_3$), argon is a noble gas with more protons and neutrons than hydrogen, and methane is a compound ($CH_4$).

Answer:

D. hydrogen