When eggs are heated, the transparent liquid portion around yolk turns solid and turbid white. This happens due to the thermal denaturation of

The correct answer is B, proteins. Egg white is mostly water and protein, and heat denatures these proteins so that they set into an opaque white solid.

The clear part of an egg, the albumen, is about 90 percent water and about 10 percent protein, chiefly ovalbumin. In the raw egg the protein chains are folded into compact shapes held by weak bonds, and they let light pass. Heat breaks these weak bonds, the chains unfold and then tangle and bond with one another, a process called coagulation. The new network traps water and scatters light, so the liquid turns firm and white. The change cannot be reversed by cooling, which is why a boiled egg stays boiled.

A is wrong because the fat of an egg is almost all in the yolk, not in the white. C is wrong because ribose is the sugar in RNA and plays no part in the setting of egg white. D is wrong because egg white contains only a trace of carbohydrate.

Exam tip: cooking an egg, curdling milk with acid and setting paneer are everyday examples of protein denaturation.