Answer is:
1: Kr.
2: Cl₂.
3: F₂.
4: O₂.
5: N₂.
6: He.
The lighter (smaller) particles move more quickly than heavier (larger) ones at the same temperature.
Calculate molar masses of the compounds:
M(Cl₂) = 70.9 g/mol; molar mass of chlorine gas.
M(F₂) = 38 g/mol, molar mass of fluorine gas.
M(He) = 4.002 g/mol; molar mass of helium.
M(Kr) = 83.8 g/mol; molar mass of krypton.
M(N₂) = 28.01 g/mol; molar mass of nitrogen gas.
M(O₂) = 32 g/mol; molar mass of oxygen gas.