Better, more refined answer for this kinetic molecular theory question?

Since you know that the lighter m molecules move faster than the heavier ones, without doing a calculation, you could just answer that the average speeds of hydrogen molecules is considerably greater than that of chlorine molecules. By the way, the equation that you derived is known as Graham's Law of effusion, and it states that the ratio of the velocities of two gaseous elements will be inversely proportional to the square roots of their molecular mes (or atomic mes for monatomic gases).