Question

as we know that on heating liquids convert into gas or became more liquid but when we heat egg then why it becomes solid????​

Answer 1

Eggs freeze when the water in them freezes. Roughly, an egg has a freezing point of [-2C; 28F) according to Oregon State University [1]. The temperature of a fridge does not drop this low (it does in the freezer), so the yolk and albumen remain as viscous liquids.

When an egg is heated or boiled, the proteins in the yolk and albumen are denatured. The existing bonds in the proteins break, and new bonds are formed. I'll refer to a blog post of the science journal Natur.

Answer 2

First of all NICE QUESTION... and

The answer is: When we heat egg the egg shell forms a more tough coating of calcium carbonate and thus it becomes hard..