Question

You put two ice cubes in a glass and fill the glass to the rim with water. As the ice melts, the water level

(a) Drops below the rim.

(b) Rises and water spills out of the glass.

(c) Remains the same.

(d) Drops at first, then rises until a little water spills out.

Short answer

The correct option is (d) drops at first, then rises until a little water spills out.

Step-by-step solution

Understanding the volume of water

Whenever a specific mass of water transforms into solid ice, the ice acquires more volume than the volume acquired by the water due to density variation with temperature. The volume of water depends on the density of water and its mass.

Explaining the variation of water level in the glass

The water level remains the same when the ice cube melts. A floating object removes the amount of water equal to its weight. As water expands when it freezes, one litre of frozen water contains more than one volume of liquid.

Therefore, the correct option is (D) drops at first, then rises until a little water spills out.

As the two ice cubes lie in the glass and the glass fills with water to its rim, there would be some volume of water displacement due to the weight of both ice cubes. The ice cubes acquire more volume (expansion takes place) compared to the volume of water from which it is made. As the ice cubes start melting, the volume of water would be less than the volume of ice cubes, so the water level first drops and then rises when ice cubes melt until a little water spills out.

Thus, from the above analysis, option (d) is correct.