Given: Volume of gas, V1 = 200 mL or 0.2 L
Pressure, P1 = 750 mm Hg
Pressure, P2 = 2 P1
Volume, V2 = ?
Solve: As we know PV = nRT
Since temperature is constant, so nRT will remain same in both cases. We can write at constant temperature
P1VI = P2V2
750×200 = 2×750 V2
V2 = 200 / 2
= 100 mL
It can also be explained according to Boyle's law that at constant temperature pressure is inversely proportional to volume of gas. If the pressure is double than volume will be reduced to half.