Use the ideal gas equation PV=nRT. You can compare before and after using P1V1/n1T1=P2V2/n2T2. Since the number of moles remains constant you can disregard moles from the equation and use pressure, volume and temp. Make sure your pressure is converted to atmospheres, your volume is in liters, and your temperature is in kelvins.
Answer: By using electrolysis.
Explanation:
Electrolysis is a chemical change produced by sending an electric current through a compound. Electrolysis works because the hydrogen and oxygen ions are held together by an electric attraction.