**Core Concept:** Chlorhexidine is a cationic bisbiguanide antiseptic with broad-spectrum antimicrobial activity. It exerts its effect by binding to the bacterial cell membrane, disrupting cell membrane integrity and causing cell death.

**Why the Correct Answer is Right:** Chlorhexidine is bactericidal, meaning it kills bacteria directly by disrupting their cell membrane and inhibiting their growth. Its concentration needs to be high enough to achieve this effect. The correct answer is not provided in the options, but we can infer its concentration from the context of the question.

**Why Each Wrong Option is Incorrect:**

A. **Incorrect** because it does not represent the concentration at which chlorhexidine is bactericidal.
B. **Incorrect** as the correct concentration is not provided, but it is less than the bactericidal concentration.
C. **Incorrect** as the correct concentration is not provided, but it is less than the bactericidal concentration.
D. **Incorrect** as the correct concentration is not provided, but it is likely less than the bactericidal concentration.

**Clinical Pearl:** The bactericidal concentration of chlorhexidine is essential for sterilization and disinfection in clinical settings. Understanding the concentration helps in preventing contamination and infection.

**Correct Answer: [Letter] [Answer Text]**

[Letter]: The correct concentration of chlorhexidine to be bactericidal is not explicitly mentioned in the options, but it should be higher than the minimum inhibitory concentration (MIC). The MIC is the lowest concentration of an antimicrobial agent that inhibits the visible growth of a microorganism. Raising the concentration above the MIC will result in bactericidal activity, leading to the direct killing of bacteria.