The substance that is used in the steel industry for the removal of carbon. Sulphur and phosphorus impurities from pig iron is

Analyze the question Pig iron from the blast furnace contains impurities such as carbon, sulphur, and phosphorus. To make steel, these must be removed. The question asks which substance does this.

Explain the concept In steelmaking (the Basic Oxygen Process, or the older Bessemer and open-hearth methods), the impurities are removed by oxidation. A stream of pure oxygen is blown through the molten pig iron. The impurities react with the oxygen to form oxides:

• Carbon: C + O₂ → CO₂ (or 2C + O₂ → 2CO), which escapes as gas
• Sulphur: S + O₂ → SO₂, which escapes as gas
• Phosphorus: 4P + 5O₂ → P₄O₁₀, which is acidic

The phosphorus oxide is acidic, so it reacts with the basic lining or flux (CaO, lime) to form slag, such as calcium phosphate. The slag floats on top of the molten steel and is removed.

Check the other options

• Chlorine: not used in steelmaking, and it would corrode the iron.
• Nitrogen: inert and unreactive here, so it cannot oxidise the impurities.
• Hydrogen: a reducing agent, so it would not remove impurities by oxidation. It can also make steel brittle.

Answer The correct option is A. oxygen.

Tip: Remember "Steel = Oxidation". Impurities in pig iron (C, S, P) are burned off with oxygen. If a question asks about removing impurities from iron, think oxygen and lime (for the slag).