Which of the following is an ore of copper?

Malachite

The correct answer is option 2. Malachite. 

Let us explore each mineral and its relevance to ore extraction:

1. Kaolinite

Kaolinite is a type of clay mineral with the formula \( \text{Al}_2\text{Si}_2\text{O}_5(\text{OH})_4 \).

Uses: It is primarily used in the production of porcelain, ceramics, and as a filler in paper and paint.

Relevance: Kaolinite is not associated with copper extraction and is not considered an ore of any metal.

2. Malachite

Malachite is a copper carbonate hydroxide mineral with the formula \( \text{Cu}_2\text{CO}_3(\text{OH})_2 \). It is known for its vibrant green color.

Uses: It is an important copper ore and is used for the extraction of copper metal. Malachite is typically found in the oxidation zones of copper deposits.

Extraction: The copper content in malachite is extracted through various methods including roasting and leaching, which eventually lead to the production of pure copper metal.

Relevance: Malachite is a primary ore of copper, making it crucial in the copper mining industry.

3. Siderite

Siderite is an iron carbonate mineral with the formula \( \text{FeCO}_3 \).

Uses: It is an important ore of iron and is used in the extraction of iron metal. Siderite is usually found in sedimentary rock formations.

Relevance: Siderite is not associated with copper extraction and is not an ore of copper.

4. Magnetite

Magnetite is an iron oxide mineral with the formula \( \text{Fe}_3\text{O}_4 \).

Uses: It is a major ore of iron and is used in the extraction of iron metal. Magnetite is known for its magnetic properties and is found in igneous and metamorphic rocks.

Relevance: Magnetite is not related to copper extraction and is not an ore of copper.

Summary

Malachite is the correct answer because it is a well-known copper ore. It is used in the extraction of copper, which involves processes like roasting and leaching to convert the copper content into usable metal. The other minerals listed are ores of different metals or used for other purposes.