If i have two balloons. 1st balloon- 2 L of Hydrogen. 2nd balloon 2 L of Oxygen which balloon is heavier? or Are they the same ?

Answer 1

From PV = nRT you can see rhat if the temperature and the pressure are constant, and we know that R is constant, then V (volume) is directly related to n (moles). Since 1 mole of oxygen is heavier than 1 mole of hydrogen, the 2nd balloon will weigh more, i.e., it will be heavier.