Final answer:
The stable gas derived from the radioactive decay of potassium-40 (40K) is argon.
Step-by-step explanation:
The stable gas derived from the radioactive decay of potassium-40 (40K) is argon (option D).
Potassium-40 (40K) undergoes beta decay to form calcium-40 (40Ca) and releases an electron and an electron antineutrino. The resulting calcium-40 then undergoes gamma decay into its ground state.
Argon is a noble gas that is nonreactive and stable. It is present in the atmosphere and is mainly produced by the radioactive decay of potassium-40 (40K) in rocks and minerals.