X and Y are two volatile liquids with molar weights of 10 g mol –1 and 40 g mol –1…

X and Y are two volatile liquids with molar weights of 10 g mol^–1 and 40 g mol^–1 respectively. Two cotton plugs, one socked in X and the other soaked in Y, are simultaneously placed at the ends of a tube of length L = 24 cm, as shown in the figure. The tube is filled with an inert gas at 1 atmosphere pressure and a temperature of 300 K. Vapours of X and Y react to form a product which is first observed at a distance d cm from the plug soaked in X. Take X and Y to have equal molecular diameters and assume ideal behaviour for the inert gas and the two vapours.
 
The experimental value of d is found to be smaller than the estimate obtained using Graham’s law. This is due to
(2014)