The deficiency symptoms of which of the following nutrients are visible first in the senescent leaves?

Options

A. Nitrogen, potassium and calcium
B. Boron, calcium and magnesium
C. Potassium nitrogen and magnesium
D. Sulphur, boron and potassium

Answer

**Step-by-Step Solution:**

1. **Understanding Nutrient Deficiency**: Nutrient deficiencies in plants can lead to visible symptoms, which are referred to as deficiency symptoms. These symptoms can manifest in various parts of the plant, depending on the nutrient involved.

2. **Identifying Actively Mobilized Nutrients**: Some nutrients can be actively mobilized within the plant. This means that when there is a deficiency, these nutrients can be moved from older tissues (like senescent leaves) to younger, developing tissues.

3. **Examples of Actively Mobilized Nutrients**: Key nutrients that are known to be actively mobilized include nitrogen, potassium, and magnesium. When these nutrients are deficient, the symptoms will first appear in the older leaves (senescent leaves) because the plant reallocates these nutrients to support new growth.

4. **Mechanism of Nutrient Mobilization**: In older leaves, the biomolecules containing these nutrients are broken down. This breakdown releases the nutrients, which are then transported to younger leaves, leading to deficiency symptoms being observed in the older leaves first.

5. **Conclusion**: Therefore, the deficiency symptoms of nitrogen, potassium, and magnesium are visible first in the senescent leaves.

**Final Answer**: The nutrients whose deficiency symptoms are visible first in the senescent leaves are nitrogen, potassium, and magnesium.

---