When you see a green ring around an egg yolk, it’s a sign that...

Role in the Reaction
Sulfur
Naturally present in egg whites (from proteins like albumin)
Iron
Found in the yolk (bound in phosvitin protein)
Heat + Time
Prolonged boiling releases sulfur as hydrogen sulfide gas
The Reaction
Hydrogen sulfide migrates to yolk → reacts with iron → forms ferrous sulfide (green-gray compound)

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