A small stone is inside an ice block, which floats in water. When the ice fully melts, the level of water
A) Increases
B) Decreases
C) Does not change
D) First decreases and then increases

Hint: Recall that the amount of space that an object occupies is known as its volume. All the objects in the universe have some volume. This is because the volume of a substance varies directly with the mass of the substance and inversely with the density of the substance.

Complete step by step answer:
Volume of an object can change with the conditions such as temperature, pressure. A small stone is inside an ice block, which floats in water. The size of the stone is much smaller than the ice cube. So its volume will also be less than the ice cube.

At ${4^ \circ }C$, water reaches its maximum density. After this temperature, if further cooled, then it gets freezed into ice. This is because below this temperature the water molecules form stronger bonds with each other. So the ice cube occupies less volume, and the level of water will decrease.

Therefore, when a small stone is placed inside an ice block and when the ice fully melts then the level of water will decrease.

Therefore option B is the right answer.

Note:
It is important to note that it is the density of the object that explains whether an object will float or sink. The density of an object is compared with that of water. If the density of an object is more than that of water, then it will sink. On the other hand, if the density is less than that of water, then it will float.