Final answer:
In angiosperms, fertilization leads to a diploid zygote and a triploid endosperm, a process called double fertilization, resulting in answer 'c. Diploid zygote and an endosperm nucleus'.
Step-by-step explanation:
In angiosperms, fertilization results in the formation of a diploid zygote and an endosperm nucleus. This process is known as double fertilization. Specifically, one sperm cell fuses with the egg to create the diploid zygote which will develop into the future embryo.
Concurrently, the second sperm fertilizes two polar nuclei, leading to the formation of a triploid endosperm nucleus. This triploid cell will develop into the endosperm, a nutritive tissue that provides food reserves for the growing embryo.
The endosperm can be particularly important in endospermic dicots, where it serves as the main food storage tissue. Therefore, the correct answer to the student's question is 'c. Diploid zygote and an endosperm nucleus'.