Final answer:
The most appropriate nursing intervention for a patient with aching at the biopsy site after a bone marrow biopsy is to administer paracetamol 500 mg po.
Step-by-step explanation:
The most appropriate nursing intervention for a patient with aching at the biopsy site after a bone marrow biopsy is to administer the ordered paracetamol 500 mg po (option a). Paracetamol, also known as acetaminophen, is a commonly used analgesic that can help relieve mild to moderate pain, such as the aching reported by the patient. It is important to provide pain relief to improve the patient's comfort and quality of life.