mass of balloon filled with water $=101 \mathrm{g}$
mass of water $=100 \mathrm{g}=\mathrm{V}_{\text {balloon }} \rho_{\mathrm{\omega}}$
when balloon is immersed in water
effective weight $=$ weight $-$ Buoyancy
$=(101) \mathrm{g}-\mathrm{V}_{\mathrm{balloon}} \rho_{\mathrm{\omega}} \mathrm{g}$
$=(101) \mathrm{g}-(100) \mathrm{g}=1 \mathrm{g}$
weight $=1 \mathrm{g}$



