Question

which substance is used to remove rust from metal?
○ lye (naoh)
○ hydrochloric acid (hcl)
○ ammonia (nh₃)
○ sulfuric acid (h₂so₄)

Explanation:

Rust is primarily iron(III) oxide ($Fe_2O_3$). Acids react with this metal oxide to form soluble salts, removing the rust. Hydrochloric acid (HCl) is commonly used for this purpose because it reacts with rust to produce soluble iron(III) chloride and water, and it is less likely to cause over-corrosion of the underlying metal compared to stronger alternatives like sulfuric acid in many rust removal applications. Lye (a base) and ammonia (a weak base) do not react with metal oxides like rust.

Answer:

hydrochloric acid (HCl)