The site of formation of pollen grains is in the :

Options

A. pistil
B. receptacle
C. petal
D. stamen

Explanation

**Step-by-Step Solution:**

1. **Understanding Pollen Grains**: Pollen grains are the male gametophytes in flowering plants. They are crucial for the reproduction process as they carry the male gametes.

2. **Identifying the Site of Formation**: Pollen grains are formed in specific structures within the flower. The question asks where this formation occurs.

3. **Analyzing the Options**:
- **Pistil**: This is the female reproductive part of the flower, which includes the ovary, style, and stigma. Therefore, it cannot be the site of pollen grain formation.
- **Receptacle**: This is the thickened part of the stem from which the flower organs arise. It does not produce pollen grains.
- **Petal**: Petals are modified leaves that often attract pollinators. They do not play a role in the formation of pollen grains.
- **Stamen**: This is the male reproductive part of the flower, consisting of two parts: the filament and the anther. Pollen grains are produced in the anther through the process of meiosis.

4. **Conclusion**: Based on the analysis of the options, the correct answer is **stamen**, as it is the site where pollen grains are formed.

**Final Answer**: The site of formation of pollen grains is in the **stamen**.

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