All are the elements whose deficiency symptoms first appear in the older tissues, except

Options

A. Nitrogen
B. Calcium
C. Potassium
D. Magnesium

Answer

To solve the question regarding which element's deficiency symptoms first appear in older tissues, we need to analyze the options provided: nitrogen, calcium, potassium, and magnesium.

### Step-by-Step Solution:

1. **Understanding Mobile vs. Immobile Elements:**
- Mobile elements are those whose deficiency symptoms first appear in older tissues. This is because they can be translocated from older to younger tissues.
- Immobile elements are those whose deficiency symptoms first appear in younger tissues. They cannot be moved from older tissues to younger ones.

2. **Identifying the Elements:**
- **Nitrogen (Option A):** Nitrogen is a mobile element. Its deficiency symptoms first appear in older tissues.
- **Calcium (Option B):** Calcium is an immobile element. Its deficiency symptoms first appear in younger tissues.
- **Potassium (Option C):** Potassium is also a mobile element. Its deficiency symptoms first appear in older tissues.
- **Magnesium (Option D):** Magnesium is a mobile element as well. Its deficiency symptoms first appear in older tissues.

3. **Analyzing the Options:**
- From the analysis, we see that:
- Nitrogen (A) - Mobile (incorrect)
- Calcium (B) - Immobile (correct)
- Potassium (C) - Mobile (incorrect)
- Magnesium (D) - Mobile (incorrect)

4. **Conclusion:**
- The element whose deficiency symptoms first appear in younger tissues (and thus is the exception in the context of the question) is **Calcium (Option B)**.

### Final Answer:
The correct answer is **Option B: Calcium**.

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