The formula of rust is Fe2O3 . x H2O. Let's understand this answer in detail.

Rust - Definition and Formation

Rust is a type of corrosion that occurs when iron or steel comes in contact with oxygen and water. It is a reddish-brown substance that forms on the surface of iron or steel objects over time. The process of rust formation can be explained as follows:

- The iron or steel object reacts with oxygen in the presence of water to form iron oxide (FeO) or hydrated iron oxide (Fe(OH)2).
- The FeO or Fe(OH)2 further reacts with oxygen and water to form Fe2O3 . x H2O, which is the chemical formula for rust.

Formula of Rust - Fe2O3 . x H2O

Now, let's look at the chemical formula of rust in detail:

- Fe2O3: This is the chemical formula for iron(III) oxide, which is also known as ferric oxide. It is a reddish-brown compound that is commonly found in nature as the mineral hematite.
- x H2O: This represents the variable amount of water molecules that can be present in rust, depending on the conditions in which it forms. The value of x can range from 0 to 9, indicating that rust can have different degrees of hydration.

Therefore, the formula of rust is Fe2O3 . x H2O, where x represents the variable amount of water molecules.

Other Options

Let's also look at the other options given in the question and why they are not the correct answer:

- Fe3O4: This is the chemical formula for magnetite, which is a black or brownish-black mineral that is magnetic. It is not the formula for rust.
- FeSO4 . 7H2O: This is the chemical formula for iron(II) sulfate heptahydrate, which is a blue-green crystalline solid. It is not the formula for rust.
- FeCl3 . x H2O: This is the chemical formula for iron(III) chloride, which is a yellow-brown solution that is used in various industrial applications. It is not the formula for rust.