Use Root mean square speed formula:
vrms = Sqrt (3RT/M)
T - temperature in K = 273K - 21CÎż = 252K
R- molar gas constant = 8.31J/Kmol
M - molar mass of a molecule
MN2 = 14x2 = 28 g/mol
MO2 = 16 x 2 = 32 g/mol
MO3 = 16 x 3 = 48 g/mol
Having all info now, you can calculate root mean square speed,vrms ,
for every molecule by using the aboveequasion and only changing M value.