Graham's Law of Effusion states that the rate of effusion of a gas is inversely proportional to the square root of its molar mass.

Molar Mass:

* Oxygen (O₂): 32 g/mol

* Argon (Ar): 40 g/mol

Calculation:

The ratio of effusion rates is given by:

```

Rate of effusion of O₂ / Rate of effusion of Ar = √(Molar mass of Ar / Molar mass of O₂)

= √(40 g/mol / 32 g/mol)

= √1.25

≈ 1.12

```

This means that molecular oxygen effuses approximately 1.12 times faster than atomic argon at the same temperature.

Conclusion:

Since oxygen has a lower molar mass than argon, it will effuse faster due to its higher average speed.