A weightless rubber balloon is filled with 200 cc of water. Its weight in water is equal to:

A 200 cc water-filled, weightless balloon contains 0.2 kg of water whose weight is mg = 0.2×9.8 = 1.96 N (i.e. 9.8/5 N). By Archimedes’ principle, the buoyant force on an object immersed in a fluid equals the weight of the fluid displaced. A water-filled balloon displaces exactly the same volume (and hence the same weight) of water as the water it contains, so the buoyant force equals 1.96 N and cancels the gravitational force on the contained water [1]. Thus the net (apparent) weight of the balloon in water is zero. Note that although it appears weightless in the fluid, its weight is transmitted to the surrounding fluid/container [2].

Sources

1. [1] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 5: Exploring Forces > A step further > p. 76
2. [2] https://en.wikipedia.org/wiki/Mass_versus_weight