Concept:Corrosion is the chemical transformation of metals into compounds like oxides, sulphides, or carbonates through reaction with environmental agents.
Explanation:During corrosion, metals lose their metallic properties and form stable compounds such as
Fe2​O3​ (rust),
CuCO3​ (patina), or
Ag2​S (tarnish).
This process involves reaction with oxygen, moisture, or sulfur compounds in the air.
Weight gain during corrosion is due to addition of oxygen or other elements, not specifically from acids — so option A is incorrect.
Melting at low temperature (option C) is a physical change, not a chemical reaction like corrosion.
Colour change (option D) is a consequence but not the defining feature; the key is the formation of new compounds.
Answer:Metals are converted to their oxide, sulphide or carbonate by reaction with environmental agents.