Question

When sugar is dissolved in water, the level of water ___?
(A) Increases
(B) Decreases
(C) Remains same
(D) Data insufficient

Answer 1

The volume of any mixture is ideally the sum of the volumes of the individual constituents of the mixture. But such an addition of volumes is observed only when there is no phase change involved and the constituents do not interact with one another. The forces of attraction or repulsion between the particles can cause significant changes in the total volume.

Complete answer:
When sugar is mixed with water, a clear solution is obtained due to the formation of a homogenous solution between sugar and water.
The sugar granules are small in size and dissociate or get fragmented further upon dissolution. Water present in its liquid state has wide empty spaces in between its molecules. It is only due to these spaces that liquids have a tendency to flow and the flexibility to change their shapes according to the containers.
When sugar particles evenly spread themselves throughout the bulk volume of water, they gradually occupy and fit inside the empty spaces present between its molecules. This process is responsible for the homogenous character of the solution. Since the sugar particles do not occupy any new spaces (that aren't already covered by water), the volume of the solution remains unchanged.
Hence, the correct option is (c) that the water level remains the same on adding sugar.

Note:
The case discussed above is an ideal case but if excess sugar is added to a limited amount of water, the empty spaces present in between water molecules would eventually fill up and the solution will become saturated. Addition of sugar beyond the saturation point would lead to an increase in the water level.