8. Hard-boiled eggs are easy to make and are a handy snack to have around the house. Just drop the whole egg into boiling water and seven minutes later you have a hardboiled egg with a soft yolk
center. The longer you cook the egg, the firmer the egg yolk becomes. When the yolk hardens, a
greyish layer of iron (ll) sulfide forms on the surface of the yolk. This compound is a result of the
iron in the yolk reacting with the hydrogen sulfide gas (H2S) released by the egg white. Hydrogen
gas (Hz) is also produced. The chemical formula for iron (II) sulfide is FeS and it is safe to eat.
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