Hormone primarily concern with cell division is

Options

A. Ethylene
B. NAA
C. Cytokinin / zeatin
D. Gibberellic acid

Answer

### Step-by-Step Solution:

1. **Identify the Question**: The question asks for the hormone that is primarily concerned with cell division in plants.

2. **Review the Options**: The options provided are ethylene, NAA (Naphthaleneacetic acid), cytokinin, obligazate, and gibberellic acid.

3. **Understand the Role of Each Hormone**:
- **Ethylene**: Primarily involved in fruit ripening and leaf abscission.
- **NAA**: A synthetic auxin that promotes root formation and growth.
- **Cytokinin**: Known to promote cell division (cytokinesis) in plant cells.
- **Obligazate**: Not a commonly recognized plant hormone related to cell division.
- **Gibberellic Acid**: Primarily involved in stem elongation, seed germination, and flowering.

4. **Focus on Cytokinin**: Cytokinin is specifically known for its role in promoting cell division. The term "cytokinin" itself derives from "cyto" meaning cell and "kinin" meaning to move or divide, which directly relates to its function in promoting cytokinesis (the division of the cytoplasm during cell division).

5. **Historical Context**: Cytokinins were first isolated from herring sperm by Miller in 1955 and were named kinetin. Later, naturally occurring cytokinins were discovered in plants, such as zeatin.

6. **Auxin's Role**: It is important to note that while cytokinins promote cell division, they often work in conjunction with auxins, another class of plant hormones, to effectively stimulate cell division.

7. **Conclusion**: Based on the information, the hormone primarily concerned with cell division is **cytokinin** (also known as zeatin).

### Final Answer:
The hormone primarily concerned with cell division is **cytokinin**.

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