Correct Option
When a weightless rubber balloon is filled with 200 cc (i.e., 200 cm³ or 0.2 liters) of water and fully submerged in water, it displaces a volume of water equal to the volume of water it contains. According to Archimedes' Principle, the upward buoyant force acting on the balloon is equal to the weight of the fluid displaced. In this specific scenario, the weight of the water inside the balloon is precisely equal to the weight of the water displaced by the balloon. Consequently, the net downward gravitational force is perfectly balanced by the upward buoyant force. Therefore, the apparent weight of the balloon filled with water, when measured in water, is zero.
Incorrect Options
Options (a), (b), and (c) suggest a non-zero net weight for the balloon in water. This is incorrect because the system described achieves a state of neutral buoyancy. Since the density of the water inside the balloon is identical to the density of the surrounding water, and the balloon itself is considered weightless, the buoyant force exactly counteracts the gravitational force. A non-zero net weight would imply either sinking or rising, which contradicts the equilibrium condition for a body of the same density as the fluid it displaces.