What is the nature of primary endosperm nucleus?

Triploid

The correct answer is Option (2) -Triploid

In double fertilization, which is a unique feature of flowering plants (angiosperms), two fertilization events occur. One fertilization event involves the fusion of one sperm cell with the egg cell, leading to the formation of the zygote, which develops into the embryo. This is the typical fertilization process that occurs in most organisms.

The second fertilization event is the fusion of the other sperm cell with the two polar nuclei present in the central cell of the embryo sac. This fusion forms a triploid (3n) cell known as the primary endosperm nucleus. This primary endosperm nucleus then undergoes several rounds of mitotic divisions to form the endosperm, which serves as a nutritive tissue for the developing embryo.

Therefore, the endosperm nucleus is triploid. The endosperm nucleus resulting from double fertilization is triploid, containing three sets of chromosomes.