This statement is very easy to be solved. As we know that Noble Gases are group of Elements which have complete valence shell and are stable elements and don't react easily and hence, are found in mono-atomic form in nature. These elements can be found on the extreme right of the periodic table in group 8 or group 18. Following are the Noble elements,
(i) Helium
(ii) Neon
(iii) Argon
(iv) Xenon
(v) Radon
Now,
In statement we are provided with only two noble gases i.e. Helium and Radon. Therefore, it is easy among them to finalize the heaviest one as Radon having atomic mass of 222.02 g/mol and atomic radii of 0.22 nm is much denser/heavier than Helium having atomic mass of 4.0 g/mol and atomic radii of 0.122 nm.
