The weight of a balloon is W ₁ when empty and W₂ when filled with air. Both are weighed in air by the same sensitive spring balance and under identical conditions.

${\mathrm{W}}_2>{\mathrm{W}}_1$, as the air inside is at a greater pressure and hence has greater density that the air outside

${\mathrm{W}}_2={\mathrm{W}}_1+$weight of the air indie it

${\mathrm{W}}_2<{\mathrm{W}}_1$ due to the force of buoyancy acting on teh filled balloon

${\mathrm{W}}_1={\mathrm{W}}_2$ as the weight of air in the balloon is offset by the force of buoyancy on it.