Question

the atom with the largest atomic radius in group 18 is -
options: he, rn, ar, kr

Explanation:

In Group 18 (noble gases), atomic radius increases as we move down the group because each successive element has an additional electron shell. The elements in Group 18 are He (Helium), Ne (not in options), Ar (Argon), Kr (Krypton), Rn (Radon), etc. Among the given options (He, Rn, Ar, Kr), Rn is the lowest in the group (has the most electron shells), so it has the largest atomic radius.

Answer:

Rn (the option with "Rn" text)