The joining of nuclei and chromosome is known as fertilization.
In vitro fertilization (IVF) is a process by which egg cells are fertilized by sperm outside the womb, in vitro.
The correct answer between all the choices given is the second choice or letter B. I am hoping that this answer has satisfied your query and it will be able to help you in your endeavor, and if you would like, feel free to ask another question.