Final answer:
Peter the Great's first wife was Eudoxia Lopukhina and she was sent to a nunnery. She was not executed but forced to take the veil and lived there until after Peter's death.
Step-by-step explanation:
Peter the Great's first wife was Eudoxia Lopukhina. The correct answer to what happened to her is a. Eudoxia, sent to nunnery. Peter was reportedly unhappy with Eudoxia and her conservative faction, who opposed his modernizing reforms. Their marriage was eventually dissolved, and in 1698, Eudoxia was forced to take the veil and was sent to a convent, which effectively served as her imprisonment until Peter's death.
The claim that she was executed is incorrect, as she outlived Peter, while the other options mentioning Natalya Naryshkina (Peter's mother) and Sophia (Peter's half-sister) pertain to different individuals in Peter's life. Natalya Naryshkina died a natural death, and it was Sophia who was sent to a nunnery after a failed bid for power.