Compute the molar mass of the unknown gas. Remember that the faster the rate of effusion, the shorter the time essential for effusion of 1.0 L; that is, rate and time are inversely proportional.
A gas of unknown molecular mass was permissible to effuse through a small opening under constant-pressure conditions. It needed 125 s for 1.0 L of the gas to effuse. In identical experimental conditions it needed 30 s for 1.0 L of gas to effuse.