For a better understanding of the Ideal Gas Equation, let us mention the four gas variables and one constant. Pressure (P), Volume (V), Number of Moles (n), and Temperature (T) are the four gas variables (T). Finally, R, often known as the Gas constant, is a constant in the equation presented below.

nRT = PV

Assume the unknown substance is x and its vapour pressure is 0.68 atm, as stated in the question.

Pressure of helium will be = 1 – 0.68 = 0.32 atm Now according to the Ideal gas Equation: PV = nRT V = nRT/P

Here, P = pressure of helium,

n = number of moles of Helium.

Now, V = 0.1×0.082×273/0.32 = **7 L**