**Core Concept**
The root value of a nerve refers to the spinal nerve root from which it originates. In the case of the radial nerve, it is a mixed nerve that carries both sensory and motor fibers from the spinal cord.

**Why the Correct Answer is Right**
The radial nerve is a continuation of the posterior cord of the brachial plexus, which is formed by the C5-C8 and T1 spinal nerve roots. However, the radial nerve itself primarily originates from the C6-C8 nerve roots. It is responsible for innervating the extensor muscles of the forearm and thumb, as well as providing sensation to the back of the hand and fingers.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because the root value of the radial nerve is not C5, although it does receive some contributions from the C5 nerve root.
**Option B:** Incorrect because the root value of the radial nerve is not T2, which is actually a contribution to the medial antebrachial cutaneous nerve.
**Option C:** Incorrect because the root value of the radial nerve is not C10, which is actually a contribution to the subscapular nerve.

**Clinical Pearl / High-Yield Fact**
The radial nerve is often injured in the radial groove of the humerus, particularly at the level of the spiral groove, due to compression or trauma.

**Correct Answer:** C. C6-C8.