Final answer:
The phase of mitosis where replicated chromosomes line up in the center of the cell is metaphase. This alignment is crucial for accurate chromosome separation into two new cells.
Step-by-step explanation:
The phase of mitosis during which replicated chromosomes line up at an invisible plane along the center of the cell is known as metaphase. During this second stage of mitosis, sister chromatids, each composed of a replicated chromosome, attach to the spindle apparatus via their kinetochores and align along the metaphase plate. This plate is an imaginary plane equidistant from the two poles of the cell where the chromosomes are maximally condensed and positioned to ensure each new cell will receive an identical set of chromosomes during cell division.