Double fertilization, which is a hallmark of angiosperm sexual reproduction, results in a a. diploid zygote and a triploid endosperm. b. haploid zygote and a triploid endosperm. c. diploid zygote and a diploid endosperm. d. haploid zygote and a diploid endosperm.

The correct answer is option A. diploid zygote and a triploid endosperm.

Explanation:

Double fertilization is a type of fertilization that is a complex mechanism takes place in angiosperms in which a female gametophyte fuse with two male gametes. In this process, pollen grains pollinate the female reproductive structure which is the stigma of the carpel.

The double fertilization process includes two male gametes, one of the gametes fuses with the egg cell and fertilizes it which forms the zygote whereas other gamete fuses with the nuclei cell which is two in number to form the endosperm.

Thus, the correct answer is option A. diploid zygote and a triploid endosperm.