The stage in which chromosomes align on the equator of spindle fiber is

The correct option is Metaphase.

Cell division is a highly organized process. During mitosis, the division of the cell nucleus is divided into four distinct active stages: Prophase, Metaphase, Anaphase, and Telophase.
Each stage has characteristic events that help in the equal distribution of genetic material:

1. Prophase: Chromatin condenses into visible chromosomes, and the spindle apparatus begins to form.

2. Metaphase: This is the stage where the spindle fibers attach to the kinetochores of the chromosomes. The spindle fibers pull and push the chromosomes until they are completely aligned along the cell's equator (also known as the metaphase plate). This alignment ensures that each new cell will receive exactly one copy of each chromosome when they separate.

3. Anaphase: The sister chromatids are pulled apart by the spindle fibers toward opposite poles of the cell.

4. Telophase: Chromosomes arrive at the poles, decondense back into chromatin, and nuclear membranes reform around each set of chromosomes.

Therefore, the stage in which chromosomes align on the equator of the spindle fiber is metaphase.