Why an egg sinks in tap water but floats in salt water

Q: Why and how did the density of water change when salt was added to it?

Ans: The water became more dense after the salt was added, as more of the mass of the water increased, compared to the volume of the water increased, when the salt is added. The formula for calculating density is mass/volume, hence when the mass increases more than the volume does, the density increases. Therefore, the water became denser when salt was added to it.

Q: Why the egg sunk in tap water but floated in salt water.

Ans: Naturally, the egg is denser than normal tap water. However, when salt is added to the water, it becomes denser than the egg, due to the reasons stated above. Since a less dense substance or objects floats on top a denser one, the egg now floats on the denser salt water.