Final answer:
The superficial radial nerve was the one likely injured during IV cannulation causing loss of sensation on the radial side of the forearm.
Step-by-step explanation:
The nerve that was likely injured during the insertion of an IV cannula in the median cubital vein, resulting in the patient losing feeling on the radial side of the forearm, is the superficial radial nerve. This nerve is responsible for providing sensation to the radial aspect of the forearm. The other options listed (A. Lateral antebrachial cutaneous, B. Medial antebrachial cutaneous, C. Musculocutaneous, D. Posterior antebrachial cutaneous) are incorrect because they either supply different areas of the arm or are not primarily sensory nerves to the forearm region. The median cubital vein is a commonly used site for venipuncture due to its superficial location and size, but care must be taken to avoid nerve injury during medical procedures.