This is an ideal gas question, so the equation PV=NKT will be used. Here P tells us Pressure, V=volume, N=number of particles, K= Boltzmann's constant and T=Temperture. The key terms in the question are Isothermal and closed system. Isothermal means that the temperature “T” is constant, while closed system tells us that the number of particles “N” is constant. Hence we can modify the ideal gas equation to this: PV=constant. This is known as Boyles law. The law says that the product of pressure and volume must be constant at all times. Therefore, we can deduce that the product of PV at the beginning of the experiment will be equal to the product of PV at the end of the experiment. PiVi=constant=PfVf. Here, “i” means initial and “f” means final. Since we have to find Pf, we will make it the subject of the formula and get this: Pf=(Pi*Vi)/Vf Pf=(1*105)/2. The answer is 5x104 Pa. So the total pressure has halved as the volume doubles.