Consider three cylinders of capacity 2.24 L each fitted with a piston, each containing 2.50 g of an ideal gas X, Y or Z as specified below at 273 K. The pressure is not specified. The molar masses (in g per mol^-1) are 40 = X, 80 = Y and 20 = Z.

The correct set of statements, 

(i) is that the number of molecules in each cylinder is the same, 

(ii) is that the average velocity of the molecules in each cylinder is the same, 

(iii) is that the pressure of gas Z is the highest and 

(iv) is that if the pressure in each cylinder is adjusted to one atmosphere at constant temperature the volume of gas Z will increase and those of the other two will decrease, is