To solve this question, we will simply use the gas law which is as follows:
PV = nRT where:
P is the pressure = 100 kPa = 0.986923 atm
V is the volume = 6.8 liters
n is the required number of moles
R is the gas constant = 0.08206
T is the temperature = 25 degree celcius (room temp) = 298 kelvin
Substitute in the above equation to get the number of moles as follows:
0.986923 x 6.8 = n x 0.08206 x 298
n = 0.2744 moles