**Given that:**

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

Pressure of gas (P_{1}) = 1 bar

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

Now,

Let P_{2} be the pressure required to compress the gas.

Therefore at constant temperature, according to Boyle’s law,

P_{1}V_{1} = P_{2}V_{2}

or, P_{2} = WV_{2}

= 1 × 500/200 = 2.5 bar

Therefore, the minimum pressure required is 2.5 bar.