is filled to a pressure of about 20,000 kPa at 300K. The volume of the tank is 26 liters. You begin to wonder, if the temperature remains constant, what would happen to the volume of the gas in the tank if its preasure increases? Which of the four processes describes this preasure- volume relationship with a constant temperature?

It would adhere to the ideal gas law where Pressure Volume and Temperature are used to calculate properties of the tank.

PV = nRT. In this case, n and R are the same.

So: (PV/T)1 = (PV/T)2

You can calculate the result of the change in pressure/volume