According to Graham's law of effusion, the ratio of the rates of effusion of two different molecules is equal to the square root of the reciprocal of the molar masses of the molecules. gas a is faster than B since it is lighter than B. Hence we expect a molar mass less than 17. we have the equation 1/0.68 = [tex] \sqrt{ \frac{17}{x} } [/tex] where x is the molar mass of gas A. This is equal to 7.86 grams.
