To solve this problem, you need to use the Ideal Gas Law equation. The Ideal Gas Law Equation is:
PV = nRT
P = the pressure (in mmHg for this question)
V = the volume (in L)
n = the number of moles of the gas
R = the Gas Constant (for this problem it is 62.36367 mmHg*L/(mol*K)
T = the temperature in Kelvin
The problem says the gas "exerts a pressure of 700. mmHg", so P = 700 mmHg. The problem asks "what is the volume of the container", so we want to find the volume. So V = what we want to find. The problem says that "0.250 moles of a gas" so we know that n = 0.250 moles. We already established that R = 62.36367 for this problem. The temperature is given to us as 25 degrees Celsius, but we need to convert it to Kelvin. We use the following conversion to convert from Celsius to Kelvin: K = 273.15 + Celsius. So K = 273.15 + 25.
So K = 298.15. Thus, T = 298.15 K.
Now we put this information into the Ideal Gas Law equation and solve for V:
PV = nRT
700 * V = 0.250 * 62.36367 *298.15
700 * V = 4,648.43205
V = 4,648.43205 / 700
So V = 6.64 liters.