[maple1234]

When solids r heated they turn into liquids, further heating change liquids into gases, then why hen’s and other bird’s eggs solidify upon heating?

[Perito]

When solids are heated, they turn into liquids. Further heating changes liquids into gases. Why, therefore, do hen’s and other bird’s eggs solidify upon heating?

Great question!

The answer is actually pretty simple but it's important to note that not all solids melt and/or evaporate.

A lot of substances decompose when they get hot. Eggs, don't decompose, but they come close. They undergo something denaturation. Eggs (especially the whites) are composed primarily of chains of protein. These proteins arrange themselves in a certain way in space. When you heat the eggs up, this "perfect" arrangement of proteins gets messed up. The chains of protein get tangled and the protein becomes denatured. The process leads to solidification of the egg.