The nuclear envelope disintegrates during

The nuclear envelope disintegrates during the prophase stage of mitosis.

Explanation:

Mitosis is a form of cell division that involves vegetative cells. The process is often referred to as equational division because the parent and the daughter cells have the same ploidy level, that is, the same amount of chromosome. Mitosis usually results in the production of two daughter cells who are genetically identical to the parent. It is an important process for organism's growth and wound healing.

Mitotic process has 4 stages at the end of which the cytoplasm of the cell divides to give rise to two distinct cells. These stages are;

The onset of division (prophase) is marked by the dissolution or disintegration of the nuclear envelope. It is a lipid bilayer membrane (also known as nuclear membrane) surrounding the nucleus which houses the genetic materials. The dissolution of the nuclear envelope makes the genetic materials to be distinctly seen as being made up of chromosomes and ensures that other stages of the division proceed as necessary.

At the metaphase, the chromosomes align at the middle (equator) of the cell, the spindles which have started forming from the prophase stage engage each chromosome at the centromere from the opposite ends.

At the anaphase stage, the spindles start shortening, pulling apart sister chromatids of the same chromosome towards opposite ends.

Migration of sister chromatids to the opposite ends completes at the telophase.

After the last stage (telophase), the chromosome condenses and the nuclear envelope reappears for each daughter cells. Thereafter, the cytoplasm divides to give rise to two independent cells.

the answer to your question is b

a. to encourage apoptosis