According to the Graham's law of effusion or diffusion, the rate of diffusion of a fixed mass of a gas is inversely proportional to the square root of its density.
Therefore, the lighter the gas, the higher the rate of effusion rate since the effusion rate of a gas is inversely proportional to the square root of its molecular mass.
In this case, Helium gas is the lightest and thus, it will diffuse faster compared to the other gases.
