The water molecules expand. When anything heats up, molecules spread further apart.
Explanation:
When a hot metal cylinder is dropped into a sample of water then heat is released by metal cylinder.
This heat is gained by water molecules and hence, they tend to gain kinetic energy. As a result, water molecules will move rapidly from one place to another. Hence, there will be increase in temperature of water.
Therefore, we can conclude that when a hot metal cylinder is dropped into a sample of water, the water molecules expand to reach the final temperature.
