Final answer:
The nurse's priority in teaching a client after a modified radical mastectomy is to monitor the incision site for signs of infection such as redness and bleeding.
Step-by-step explanation:
The nurse should plan to teach the client following a modified radical mastectomy to observe for signs of infection and healing at the incision site, such as redness and bleeding, which is the correct response indicated by option B. Postoperative care also includes teaching the client how to care for drains, if present, looking for signs of infection, such as tenderness, warmth, redness, or discharge, arm exercises to promote lymphatic drainage and prevent lymphedema, as well as handling post-surgical pain and discomfort. Keeping the arm elevated could reduce swelling, and supporting the arm with pillows may be comfortable, but the most critical early postoperative education is regarding infection monitoring and wound care.