Which one contains both Ca and Mg ?

Options

A. Limestone
B. Dolomite
C. Chalk
D. Feldspar

Answer

To determine which option contains both calcium (Ca) and magnesium (Mg), we can analyze each of the given options:

1. **Limestone**:
- Composition: Primarily composed of calcium carbonate (CaCO₃).
- Contains: Calcium (Ca) but does not contain magnesium (Mg).

2. **Dolomite**:
- Composition: Composed of calcium magnesium carbonate (CaMg(CO₃)₂).
- Contains: Both calcium (Ca) and magnesium (Mg).

3. **Chalk**:
- Composition: A form of limestone, primarily made up of calcium carbonate (CaCO₃).
- Contains: Calcium (Ca) but does not contain magnesium (Mg).

4. **Feldspar**:
- Composition: A group of minerals that contain aluminum silicates with varying amounts of potassium, sodium, and calcium.
- Contains: Calcium (Ca) but does not contain magnesium (Mg).

Based on the analysis, the only option that contains both calcium and magnesium is **Dolomite**.

### Final Answer:
The correct option is **2. Dolomite**.