Answer
(a) The pressure inside the balloon is higher than the pressure outside the balloon. It is this pressure difference which keeps the balloon inflated.
(b) The air inside the balloon is less dense than the air outside the balloon because the air inside the balloon is at a higher temperature.
Work Step by Step
(a) The pressure inside the balloon is higher than the pressure outside the balloon. It is this pressure difference which keeps the balloon inflated. If we poked a hole in the side of the balloon, the air inside the balloon would come out through the hole since air moves from higher pressure to lower pressure.
(b) The air inside the balloon is less dense than the air outside the balloon because the air inside the balloon is at a higher temperature. It is this difference in density which gives the balloon its buoyancy and allows the balloon to float in the air according to Archimedes' principle.
