Question

Which is the heaviest naturally occurring noble gas?

• A. Radon
• B. Xenon
• C. Helium
• D. Argon

Hint:

Recall that atomic mass increases as you go down group 18 of the periodic table.

Answer 1

The Correct Option is A

Step 1: Noble gases sit in group 18 of the periodic table. Going down the group, atomic mass increases steadily.

Step 2: The order by atomic mass is helium, neon, argon, krypton, xenon and then radon. Radon has an atomic mass of about 222, which is higher than xenon's 131, argon's 40 and helium's 4.

Step 3: Radon occurs naturally as a decay product of radium and uranium in rocks and soil. It is radioactive and can build up in basements, so it is a real, naturally found gas, not just a lab made one.

Step 4: Helium and argon are much lighter and are common everyday examples, so students often guess them, but they are not the heaviest. Xenon is heavier than argon and helium but still lighter than radon.

Step 5: So among the given choices, radon is the correct answer.