**Core Concept**
Froment's sign is a clinical test used to assess the integrity of the ulnar nerve, specifically the adductor pollicis muscle, which is innervated by the ulnar nerve. This test is crucial in diagnosing ulnar nerve palsy or injury.

**Why the Correct Answer is Right**
Froment's sign is positive when the patient is unable to adduct the thumb (opponens pollicis) against resistance, but can do so by flexing the thumb (flexor pollicis longus) to compensate. This compensation indicates involvement of the ulnar nerve, which supplies the adductor pollicis muscle. The ulnar nerve injury or palsy leads to weakness or paralysis of the adductor pollicis muscle, resulting in a positive Froment's sign.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Froment's sign is not related to median nerve palsy, which affects the flexor pollicis longus muscle.
**Option B:** This option is incorrect because Froment's sign does not assess the function of the flexor carpi radialis muscle.
**Option C:** This option is incorrect because Froment's sign does not involve the ulnar nerve's function in the forearm or wrist.

**Clinical Pearl / High-Yield Fact**
A positive Froment's sign is a classic clinical indicator of ulnar nerve palsy, often seen in patients with cubital tunnel syndrome or a direct blow to the ulnar nerve at the elbow.

**Correct Answer:** C.