Volume of the gas,
V1 = 500 dm3
Pressure of the gas
p1 = 1 bar
Volume of the compressed gas,
V2 = 200 dm3
Let p2 be the pressure required to compressed the gas. Then at constant temperature
p1V1 = p2V2
or, p2 = {p1V1}/{V2}
= {1 bar x 500 dm3}/{200 dm3} = 2.5 bar