Which of the following does not contain phosphorus?

Phosphorus is a vital non-metallic element found in many organic and inorganic compounds. It is an essential component of all living cells and is mainly present in the body as phosphates. In biological systems, phosphorus plays a key role in energy transfer, bone structure, and cellular activity.

In the yolk of an egg, phosphorus occurs in the form of phospholipids and organic phosphates. These compounds are crucial for energy metabolism and the structural integrity of cell membranes. Egg yolk is rich in lecithin, a phospholipid that contains both phosphorus and fatty acids.

Bones contain a large amount of phosphorus combined with calcium, forming calcium phosphate (Ca₃(PO₄)₂), which gives bones strength and rigidity. About 85% of the phosphorus in the human body is stored in bones and teeth.

Nerves also contain phosphorus, mainly in the form of phospholipids that make up nerve cell membranes. Phosphorus-based compounds help maintain the electrical potential necessary for nerve impulse transmission.

On the other hand, steel is an alloy primarily composed of iron and carbon, sometimes mixed with small amounts of other metals like chromium, nickel, or manganese to enhance its properties. It does not naturally contain phosphorus as a structural component, although trace impurities of phosphorus can sometimes be present during production. These traces are considered undesirable because they can make steel brittle.

Therefore, while egg yolk, bone, and nerves all contain significant amounts of phosphorus as an essential element for biological function, steel does not contain phosphorus as a natural or functional constituent. This makes steel the correct answer.