The yellowing of leaves, called chlorosis, is usually caused by the deficiency of :

Options

A. sodium
B. phosphorus
C. magnesium
D. calcium

Answer

To solve the question regarding the yellowing of leaves, known as chlorosis, we need to analyze the role of each mineral mentioned in the options: sodium, phosphorus, magnesium, and calcium.

### Step-by-Step Solution:

1. **Understanding Chlorosis**:
- Chlorosis is the yellowing of leaves due to insufficient chlorophyll production. This condition can arise from various nutrient deficiencies.

2. **Analyzing Sodium (Na)**:
- Sodium is not a primary nutrient for plants and primarily affects growth rather than chlorophyll production. Therefore, sodium deficiency is not typically associated with chlorosis.
- **Conclusion**: Sodium deficiency does not cause chlorosis.

3. **Analyzing Phosphorus (P)**:
- Phosphorus is crucial for energy transfer and photosynthesis. While its deficiency can lead to discoloration, it does not specifically cause chlorosis.
- **Conclusion**: Phosphorus deficiency does not primarily result in chlorosis.

4. **Analyzing Magnesium (Mg)**:
- Magnesium is a vital component of chlorophyll. A deficiency in magnesium leads to intervenal chlorosis, where the leaf veins remain green while the areas between them turn yellow.
- **Conclusion**: Magnesium deficiency is directly linked to chlorosis.

5. **Analyzing Calcium (Ca)**:
- Calcium is important for cell wall structure and stability. Its deficiency can lead to tissue necrosis (death) but does not cause chlorosis.
- **Conclusion**: Calcium deficiency does not cause chlorosis.

6. **Final Answer**:
- Based on the analysis, the mineral that causes chlorosis due to its deficiency is **Magnesium**.