Question 3
When the mouth of an air-filled balloon is loosened and released, the balloon shoots upwards. Which is the reaction force that drives it up?
The right answer is the one marked above.
The air particles pushing the balloon upwards. The force applied to the balloon is the reaction.
Action: the balloon's rubber walls push the air particles downwards. Reaction: the escaping air particles push the balloon upwards.
So the balloon does not rise with nothing pushing it — the escaping air is what pushes it. Gravity acts too, but it is not the force carrying the balloon up.