Two Moles of an Ideal Gas Have an Initial Kelvin

Multiple Choice

Two moles of an ideal gas have an initial Kelvin temperature Ti and absolute pressure Pi. The gas undergoes a reversible isothermal compression from an initial volume Vi to a final volume 0.5Vi.
-Which one of the following expressions represents the final pressure of the gas?

A) 0.5P_i
B) P_i/31.7
C) 2P_i
D) 3.17P_i
E) 4P_i