Given that:
Volume of gas (V1) = 500 dm3
Pressure of gas (P1) = 1 bar
Volume of compressed gas (V2) = 200 dm3
Now,
Let P2 be the pressure required to compress the gas.
Therefore at constant temperature, according to Boyle’s law,
P1V1 = P2V2
or, P2 = WV2
= 1 × 500/200 = 2.5 bar
Therefore, the minimum pressure required is 2.5 bar.