Answer:
The correct answer is - option B. Prophase.
Step-by-step explanation:
During the late prophase of the starting of the mitosis cell division, the nuclear envelope or nuclear membrane begins to break down. However, the process of disappearing the membrane starts with the beginning of the prophase but it completely breaks down by the end of the prophase.
This breakdown of the nuclear envelope and other major cell organelle takes place to accommodate the chromosome condensed by the spindle apparatus, it also provides more space for the separation of chromatids and performing karyokinesis.
Thus, the correct answer is - option B. Prophase.