Final answer:
During amphimixis, the male and female pronuclei fuse to complete the process of fertilization, resulting in the formation of a diploid zygote, which signifies the unification of haploid gametes.
Step-by-step explanation:
During amphimixis, the male and female pronuclei fuse, which is described by answer option c. The ovum, being the female gamete, completes meiosis II following fertilization by a sperm. This completion of meiosis II results in the formation of one large ovum with the unneeded genetic material being ejected as the second polar body. Thus, the ovum becomes a haploid cell ready to unite with the sperm's haploid genetic material. Upon fusion of the male and female pronuclei during fertilization, a diploid zygote is formed. It is important to note that the process of capacitation prepares sperm to fertilize the ovum by enhancing their motility and altering the sperm membrane to facilitate the penetration of the oocyte upon contact.