Which of the following ore does not contain iron?

Carnelite

The correct answer is option 3. Carnelite.

Here is a detailed explanation of the ores mentioned and why carnelite does not contain iron:

1. Limonite:

Composition: Limonite is a mixture of hydrated iron(III) oxide-hydroxides in varying composition.

Formula: Generally represented as \(FeO(OH)·nH_2O\).

Iron Content: It is an important iron ore, containing iron in the form of iron(III) oxide-hydroxide.

Use: Mined primarily for iron extraction.

2. Siderite:

Composition: Siderite is an iron carbonate mineral.

Formula: \(FeCO_3\).

Iron Content: Contains iron in the form of iron(II) carbonate.

Use: Mined as an iron ore, siderite is another important source of iron.

3. Carnelite:

Composition: Carnelite is a potassium and magnesium chloride mineral.

Formula: \(KMgCl_3·6H_2O\).

Iron Content: Does not contain iron. Instead, it consists of potassium (K), magnesium (Mg), and chloride (Cl) ions.

Use: Mined primarily for potassium and magnesium, often used in fertilizers and in various industrial processes.

4. Chalcopyrite:

Composition: Chalcopyrite is a copper iron sulfide mineral.

Formula: \(CuFeS_2\).

Iron Content: Contains iron, but it is primarily valued for its copper content.

Use: Mined mainly for copper extraction, though it contains iron as well.

Why Carnelite Does Not Contain Iron:

Carnelite \((KMgCl_3·6H_2O)\) is a mineral composed of potassium, magnesium, and chloride. It is a significant source of potassium and magnesium but contains no iron in its chemical structure. This differentiates it from the other minerals listed (limonite, siderite, and chalcopyrite), all of which contain iron and are mined for their iron content to varying extents. Carnelite's primary uses are in the production of fertilizers, where potassium is an essential nutrient, and in other industrial applications that require potassium or magnesium compounds.