The acid that is used to remove rust is

Correct Answer: Hydrochloric acid

Explanation:

• Rust is hydrated iron(III) oxide, formed when iron reacts with oxygen and water.
• Hydrochloric acid (HCl) is commonly used to remove rust because it reacts with the iron oxide, dissolving it and leaving a clean metal surface.
• The reaction produces soluble iron chloride, which can be washed away.
• The other acids listed (boric acid, nitric acid, sulphuric acid) are not typically used for rust removal.

Therefore, the acid used to remove rust is hydrochloric acid.