The question refers to the principle of buoyancy, which means that an object fully or partly immersed in fluid experiences an upthrust or buoyant force equal to the weight of the fluid displaced. When a balloon filled with water is immersed into water, it displaces an amount of water equivalent to its own volume - in this case, 200 cc. The weight of this displaced water in terms of gravitational pull is equal to the weight of the balloon under these conditions. Since both weights are identical, they cancel out each other, resulting in a net weight of the balloon in water to be zero option - 4.
Other options, (9.8/5) N, (9.8/10) N and (9.8/2) N, are represented as specific measurements of Newton (N) - the metric unit of force in physics. These options would not apply in this context as the weight of any object will be zero when fully immersed in a fluid of similar density.