In deficiency of nitrogen, which leaves show chlorosis first?

Explanation

**Step-by-Step Solution:**

1. **Understanding Nitrogen's Role**: Nitrogen is an essential nutrient for plants, crucial for the synthesis of proteins, nucleic acids, and plant hormones. Its presence is vital for overall plant health and growth.

2. **Identifying Chlorosis**: Chlorosis refers to the yellowing of leaves due to insufficient chlorophyll production, which often occurs when there is a deficiency of essential nutrients, including nitrogen.

3. **Nutrient Mobility in Plants**: In plants, nutrients are not uniformly distributed. Instead, they are often moved from older parts of the plant to younger parts. This means that when there is a deficiency of a nutrient, the plant will first utilize the stored nutrients in older leaves to support the growth of younger leaves.

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