**Core Concept**
Phossy jaw is a historical occupational disease caused by the inhalation of phosphorus vapors, leading to necrosis of the jawbone. It was prevalent among workers in the matchstick industry.

**Why the Correct Answer is Right**
Phossy jaw is a classic example of a chemical burn to the mucous membranes of the oral cavity, which eventually leads to necrosis. The phosphorus vapors react with the water in the mucous membranes to form phosphoric acid, causing severe tissue damage. The resulting inflammation and necrosis of the jawbone can lead to severe pain, swelling, and deformity.

**Why Each Wrong Option is Incorrect**
**Option A:** Arsenic poisoning is associated with 'raindrop pigmentation' on the skin and 'mees lines' on the nails, but not phossy jaw.
**Option B:** Lead poisoning is associated with 'lead lines' on the gums and peripheral neuropathy, but not phossy jaw.
**Option C:** Mercury poisoning is associated with 'pink disease' or acrodynia in children, but not phossy jaw.

**Clinical Pearl / High-Yield Fact**
Phossy jaw is a classic example of an occupational disease that can be prevented with proper ventilation and the use of personal protective equipment (PPE) in industries handling hazardous chemicals.

**Correct Answer: C. Mercury poisoning is associated with 'pink disease' or acrodynia in children, but not phossy jaw.