An important ore of magnesium is

Options

A. Malachite
B. Cassiterite
C. Carnallite
D. Galena

Answer

To identify an important ore of magnesium, we can analyze the given options one by one.

1. **Option 1: Malachite**
- Malachite is known to be a copper carbonate hydroxide mineral. Its chemical formula is CuCO₃·Cu(OH)₂. Since it primarily contains copper and does not contain magnesium, it cannot be classified as an ore of magnesium.

2. **Option 2: Cassiterite**
- Cassiterite is recognized as the primary ore of tin, with the chemical formula SnO₂. Since it is an ore of tin and does not contain magnesium, this option is also incorrect.

3. **Option 3: Carnalite**
- Carnalite is a hydrated potassium magnesium chloride with the formula KMgCl₃·6H₂O. This mineral contains magnesium and is indeed used to extract magnesium metal. Therefore, carnalite is a valid ore of magnesium.

4. **Option 4: Galena**
- Galena is the natural mineral form of lead sulfide, with the formula PbS. Since it is an ore of lead and does not contain magnesium, this option is incorrect.

Based on the analysis of all the options, the important ore of magnesium is **Carnalite**.

**Final Answer: Carnalite**