Volume of gas(V1) = 500dm3 (given)
Pressure of gas (p1) = 1 bar (given)
Volume of compressed gas (V2) = 200dm3 (given)
Now ,let P2 be the pressure required to compress the gas.
Therefore at constant temperature P1 V1 = P2 V2(Boyle’s Law)
As a result P2 = P1 V1 / V2 = 1 X 500/200 = 2.5 bar
Therefore, the minimum pressure required is 2.5 bar.