How many nucleus participates in process of double fertilisation ? 

B. 5

Reason: In Angiosperms double fertilization takes place, the first fusion is between the egg cell and the sperm cell to form the embryo, this process is known as syngamy. The second fusion occurs between the male gamete fuse with two polar nuclei or secondary nucleus to form the endosperm. So a total of two sperm nuclei, one egg cell nuclei and two polar nuclei are involved in double fertilization.