In which phase of mitosis do chromosomes line up in the middle of the cell?

During mitosis, chromosomes align at the equatorial plane of the cell during metaphase. This phase follows prophase, where the chromatin condenses into visible chromosomes, and the mitotic spindle begins to form, attaching to the chromosomes at their centromeres.

Metaphase is characterized by the chromosomes being pulled by spindle fibers into position along the metaphase plate, which ensures that when the cell divides, each daughter cell will receive an equal and identical set of chromosomes. This precise alignment is critical for the fidelity of genetic material distribution during cell division.

The other phases do not involve this specific alignment of chromosomes. In prophase, the chromosomes condense but are not yet lined up. During anaphase, the sister chromatids are pulled apart toward opposite poles of the cell, and in telophase, the chromosomes begin to de-condense, and the nuclear envelope starts to reform. Therefore, the focus on chromosome alignment in the center of the cell distinctly identifies metaphase as the correct answer.