"a gaseous mixture contains 414.0 torr of h2(g), 345.7 torr of n2(g), and 80.1 torr of ar(g). calculate the mole fraction, x, of each of these gases."

The gaseous mixture contains 414.0 torr of h2(g), 345.7 torr of n2(g), and 80.1 torr of ar(g). Then, total pressure of the gas would be: 414 torr + 345.7 torr + 80.1 torr= 839.8 torr
The mole fraction of each gas:
H2= 414 torr/839.8 torr= 0.49
N2= 345.7 torr/839.8 torr= 0.41
Ar= 80.1 torr/839.8 torr= 0.10

True, the standard unit for volume is liters which can be represented by either a lower case "l" or a capital "l"