Hormone which helps to produce new leaves, chloroplasts in leaves, lateral shoot growth and adventitious shoot formation.

Answer

**Step-by-Step Solution:**

1. **Understanding Plant Hormones**: Start by recognizing that plant hormones, also known as phytohormones, are crucial in regulating various aspects of plant growth and development.

2. **Identifying Functions**: The question specifies several functions: production of new leaves, formation of chloroplasts, lateral shoot growth, and adventitious shoot formation.

3. **Linking Functions to Hormones**: Among the various plant hormones, each has specific roles. For instance:
- Auxins are primarily involved in cell elongation and apical dominance.
- Gibberellins promote stem elongation and seed germination.
- Ethylene is associated with fruit ripening and leaf abscission.
- Abscisic acid primarily helps in stress responses and dormancy.

4. **Focusing on Cytokinins**: Cytokinins are known to promote cell division (cytokinesis) and are particularly influential in:
- Stimulating the production of new leaves.
- Promoting the formation of chloroplasts in leaves.
- Encouraging lateral shoot growth.
- Facilitating adventitious shoot formation.

5. **Conclusion**: Based on the functions mentioned in the question, the hormone that fulfills all these roles is **cytokinin**.

**Final Answer**: The hormone which helps to produce new leaves, chloroplasts in leaves, lateral shoot growth, and adventitious shoot formation is **cytokinin**.

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