Primary Endosperm Nucleus is the product of:

The correct option is Triple fusion.

In angiosperms (flowering plants), a unique process called double fertilization occurs within the embryo sac. During this process, one of the two male gametes fuses with the egg cell to form a diploid zygote, which eventually develops into the embryo. This fusion is known as syngamy.

Meanwhile, the second male gamete, which is haploid (n), moves towards the center of the embryo sac and fuses with the diploid secondary nucleus (or two haploid polar nuclei, n + n). Because this process involves the fusion of three haploid nuclei (one male gamete and two polar nuclei), it is termed triple fusion.

The result of triple fusion is the formation of a triploid (3n) nucleus called the Primary Endosperm Nucleus (PEN). The PEN subsequently develops into the endosperm, a nutrient-rich tissue that provides nourishment to the developing embryo. Therefore, the Primary Endosperm Nucleus is the direct product of triple fusion.