**Core Concept**
Proper cleaning of the operating site before giving composite restorations is crucial to prevent contamination and ensure a successful outcome. This involves using an antimicrobial solution to eliminate bacteria and other microorganisms that may be present on the surface of the tooth or surrounding tissues.

**Why the Correct Answer is Right**
The correct answer is **C. 0.5% sodium hypochlorite (NaOCl)**. This solution is an effective antimicrobial agent that can kill a wide range of bacteria, viruses, and fungi. It works by releasing hypochlorous acid, which disrupts the cell membranes of microorganisms and ultimately leads to their death. Sodium hypochlorite is commonly used in dental procedures, including cleaning the operating site before giving composite restorations.

**Why Each Wrong Option is Incorrect**
**Option A:** **Chlorhexidine** is an antimicrobial agent, but it is not typically used to clean the operating site before composite restorations. It is more commonly used as a mouthwash or to disinfect dental instruments.

**Option B:** **H2O2 (Hydrogen Peroxide)** is a weak antimicrobial agent and is not effective against a wide range of microorganisms. It is also not typically used to clean the operating site before composite restorations.

**Option D:** **Betadine (Povidone-Iodine)** is an antimicrobial agent, but it is not typically used to clean the operating site before composite restorations. It is more commonly used as a skin disinfectant or to prepare the skin for surgical procedures.

**Clinical Pearl / High-Yield Fact**
When using sodium hypochlorite to clean the operating site, it's essential to dilute it to 0.5% concentration and use it for a limited time to avoid damaging the tooth structure or surrounding tissues.

**Correct Answer: C. 0.5% sodium hypochlorite (NaOCl)**