We can use the Ideal Gas Law to solve this problem:
PV = nRT
where P is pressure, V is volume, n is the number of moles of gas, R is the gas constant (0.08206 L·atm/K·mol), and T is the temperature in Kelvin.
First, let's convert the pressure to units of atmospheres:
0.982 atm
Now, let's convert the volume to units of liters:
21 L
And let's convert the temperature to Kelvin by adding 273.15:
288.0 K + 273.15 = 561.15 K
Now we can plug these values into the Ideal Gas Law and solve for n:
PV = nRT
n = PV/RT
n = (0.982 atm) x (21 L) / (0.08206 L·atm/K·mol x 561.15 K)
n = 0.989 mol
Therefore, there are approximately 0.989 moles of gas in the sample.