Double fertilization is said to occur in flowering pants because

Double fertilization is a unique process that occurs in flowering plants during sexual reproduction. In this process, two sperm cells from a single pollen grain fertilize two different nuclei in the female reproductive structure of the flower. The first sperm fertilizes the egg cell, forming a zygote, which eventually develops into an embryo. The second sperm fuses with the polar nuclei, which results in the formation of the endosperm. The endosperm is a food-rich tissue that provides nourishment to the developing embryo. So, the correct option is "one embryo and endosperm nucleus are formed." Double fertilization leads to the formation of both an embryo and the endosperm, which provides nutrients for the developing embryo to grow into a mature seed.