Formation of cell plate starts at

The correct answer is telophase.

Step-by-step Explanation:

1. Understanding Cytokinesis in Plants:
In plant cells, cytokinesis (the division of the cytoplasm) occurs differently than in animal cells because of the rigid cell wall. Instead of forming a cleavage furrow, plant cells synthesize a new cell wall between the two daughter nuclei. This process starts with the formation of a structure called the cell plate.

2. Initiation of the Cell Plate:
During late anaphase and early telophase, vesicles derived from the Golgi apparatus align along the equatorial plane (metaphase plate) of the cell.

3. Fusion and Growth:
These vesicles fuse together in the center of the cell to initiate the formation of the cell plate. The cell plate then grows centrifugally (from the center outward) until it reaches and fuses with the existing lateral plasma membrane and cell wall, thereby dividing the parent cell into two daughter cells.

4. Eliminating Incorrect Options:
- G₂ phase and S phase are parts of interphase where DNA replication and cell growth occur, long before chromosome segregation or division begins.
- Prophase is the first stage of mitosis, characterized by chromosome condensation and spindle formation, not cell division.
- Therefore, the formation of the cell plate begins specifically during the final stage of mitosis, which is telophase.