**Core Concept**
Sodium hypochlorite is a commonly used endodontic irrigant, but its high pH and oxidative properties can cause chemical burns, tissue damage, and toxicity if not handled properly. This hazardous irrigant requires careful management to prevent emergency situations.

**Why the Correct Answer is Right**
Sodium hypochlorite is a strong alkaline solution (pH 12-13) that can cause severe chemical burns, corrosion of instruments, and damage to surrounding tissues if not diluted correctly. Its high oxidative potential can lead to the release of toxic chlorine gas, causing respiratory distress and other systemic complications. The high pH also disrupts the cell membrane, leading to cell death and tissue damage.

**Why Each Wrong Option is Incorrect**
**Option A:** Saliva is a biologically active fluid containing enzymes, antimicrobial peptides, and other components that facilitate oral health. It is not a hazardous irrigant and is generally considered safe for treatment.

**Option B:** Chlorhexidine is an antimicrobial agent used in various dental applications, including mouthwashes and irrigants. While it can cause staining and other side effects, it is not typically considered hazardous in the same way as sodium hypochlorite.

**Option D:** Metrogyl (metronidazole) is an antibiotic used to treat various infections, including those affecting the oral cavity. It is not typically used as an irrigant and is not considered hazardous in the context of this question.

**Clinical Pearl / High-Yield Fact**
When handling sodium hypochlorite, always dilute it with water according to the manufacturer's instructions to prevent chemical burns and other complications. Additionally, wear protective gear, including gloves and eyewear, to minimize exposure risks.

**Correct Answer:**
✓ Correct Answer: C. Sodium Hypochlorite