Answer
$CH_{2}Cl_{2}\lt Kr\lt N_{2}\lt CH_{4}$
Work Step by Step
Average molecular speed $\bar{u}\propto \sqrt \frac{T}{M}$ where T is the temperature and M is the molecular weight.
Since T is same(25°C), average molecular speed is large for gases with small M.
Based on molecular weight M, we can arrange the gases in the order
$CH_{4}$(16.04 g/mol)$\lt N_{2}$(28.0 g/mol)$\lt$Kr(83.798 g/mol)$\lt CH_{2}Cl_{2}$(84.93 g/mol)
This implies that the increasing order of average molecular speed is
$CH_{2}Cl_{2}\lt Kr\lt N_{2}\lt CH_{4}$
