Answer
$CH_{2}Cl_{2}\lt Kr\lt N_{2}\lt CH_{4}$
Work Step by Step
At the same temperature, heavier gas molecules have slower average speeds. The order of gases according to molar mass is
$CH_{4}(16.04\,g)\lt N_{2}(28.0\,g)\lt Kr(83.798\,g)\lt CH_{2}Cl_{2}(84.93\,g)$
Therefore, in order of increasing average molecular speed, we find:
$CH_{2}Cl_{2}\lt Kr\lt N_{2}\lt CH_{4}$
