The weight of a balloon is W1 when empty and W2 when filled with air. Both are weighed in air by the same sensitive spring balance and under identical conditions.
(a) W1 = W2, as the weight of air in the balloon is offset by the force of buoyancy on it.
(b) W2 < W1 due to the force of buoyancy acting on the filled balloon.
(c) W2 > W1, as the air inside is at a greater pressure and hence has greater density than the air outside.
(d) W2 = W1 + weight of the air inside it.
