Question

"during which phase of mitosis does the nuclear membrane dissolve completely and the chromatid pairs arrange themselves in a single file?"

Answer 1

The answer is metaphase. It is marked by the arrangement of chromosomes at the center of the cell, half way between each of the mitoic spindle poles. Movement is intermediated by the kinetochore microtubles, which push and pull on the chromosomes to align them into what is called the metaphase plate. The chromosomes on the metaphase plate are held there firmly by pushing and pulling forces from the microtubules. Cells can stop in metaphase for days until the chromosomes are properly aligned and the cell go in anaphase.