Assertion: Formation of rust is a chemical change. Reason: For formation of rust, iron must be exposed to air and water.
Answers
Answer:
the assertion and reason are true and reason is the correct explanation of the assertion
Answer:
Rust is an iron oxide, usually reddish-brown oxide formed by reaction of iron and oxygen in catalytic presence of water and air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and the iron(III) oxide-hydroxide (FeO(OH), Fe(OH)3), and is typically associated with corrosion of refined iron.
Given sufficient time, any iron mass, in presence of water and the oxygen, could eventually convert entirely to the rust. Surface rust is commonly flaky and friable, and provides no passivational protection to underlying iron, unlike formation of patina on the copper surfaces. Rusting is the common term for corrosion of elemental iron or its alloys such as steel. Many other metals undergo similar corrosion, but resulting oxides are not commonly called "rust".
Several forms of rust are the distinguishable both visually and by spectroscopy, and form under the different circumstances. Other forms of rust include the result of reactions between iron and chloride in environment deprived of the oxygen. Rebar used in the underwater concrete pillars, which generates green rust, is an example. Although rusting is generally the negative aspect of iron, a particular form of rusting, known as the stable rust, causes the object to have a thin coating of rust over top. If kept in low and relative humidity, it makes "stable" layer protective to the iron below, but not to the extent of other oxides such as aluminium oxide on the aluminium.
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