Volume of gas(V_{1}) = 500dm^{3} (given)

Pressure of gas (p_{1}) = 1 bar (given)

Volume of compressed gas (V_{2}) = 200dm^{3} (given)

Now ,let P_{2} be the pressure required to compress the gas.

Therefore at constant temperature P_{1} V_{1} = P_{2} V_{2}(Boyle’s Law)

As a result P_{2} = P_{1} V_{1} / V_{2} = 1 X 500/200 = 2.5 bar

Therefore, the minimum pressure required is 2.5 bar.