Final answer:
The nurse should document 'C. Vertex' in the medical record for a fetus in the right occiput anterior position, which is a common and favorable position for vaginal delivery.
Step-by-step explanation:
A nurse caring for a client who is in labor has performed a vaginal examination and found the following: 2cm dilation, 50% effacement, +1 station, and the fetus is in the right occiput anterior (ROA) position. This information indicates that the fetus is positioned head down with the back of its head facing the right side of the mother's pelvis and the face pointing towards the left thigh, which means the fetus is in the vertex presentation. As such, the nurse should document "C. Vertex" in the medical record. The ROA position is favorable for vaginal birth and is one of the most common and easiest positions for the fetus to be delivered vaginally.