Answer
On average, argon atoms move faster than krypton atoms at the same temperature.
Work Step by Step
Having the same temperature means they have the same average translational kinetic energy per molecule. $KE = \frac{1}{2} mv^{2}$.
We may check the atomic masses in the periodic table (page 216) and verify that the mass m of an argon atom is much less than that of a krypton atom, so the speed v must be greater to have the same average kinetic energy.
