Answer:
He
Explanation:
Helium will have the highest speed at the given temperature value because it has the lowest molecular mass.
According to Graham's law of diffusion "the rate of effusion or diffusion of a gas is inversely proportional to the square root of its molecular mass or density at constant temperature and pressure".
In short, a gas with low molecular mass can diffuse or effuse more rapidly than one with a high molecular mass under the same condition.
Molecular mass of He = 4.0026g/mol
Kr = 83.789g/mol
Ne = 20.1797g/mol
Ar = 39.948g/mol
He has the lowest molecular mass of the given choices.
