**Core Concept**
Chlorhexidine is a disinfectant and antiseptic agent widely used in various medical and dental applications, including root canal irrigation. Its effectiveness against a broad spectrum of microorganisms, including bacteria and viruses, is due to its unique chemical structure and mechanism of action.

**Why the Correct Answer is Right**
Chlorhexidine is a broad-spectrum antimicrobial agent that exhibits activity against both Gram-positive and Gram-negative bacteria, as well as some viruses with lipid envelopes. This is due to its ability to bind to negatively charged microbial cell membranes, disrupting their structure and ultimately leading to cell death. Chlorhexidine's effectiveness against a wide range of microorganisms makes it an ideal choice for root canal irrigation, where the goal is to eliminate all residual bacteria and microorganisms from the canal system. The 2% concentration of chlorhexidine is commonly used in dental applications, including root canal irrigation, due to its optimal balance of antimicrobial activity and safety for human tissues. Furthermore, chlorhexidine is a polybiguanide, a class of compounds that have been shown to exhibit potent antimicrobial activity.

**Why Each Wrong Option is Incorrect**
**Option A:** While chlorhexidine is indeed active against Gram-positive and Gram-negative bacteria, its activity against viruses is more limited and generally restricted to those with lipid envelopes. This statement is partially correct but not entirely accurate.
**Option B:** The 2% concentration of chlorhexidine is indeed commonly used in dental applications, but it is not the only concentration used. Other concentrations, such as 0.12% and 0.2%, may also be employed depending on the specific application and desired level of antimicrobial activity.
**Option C:** Chlorhexidine is indeed a polybiguanide, but this statement is not particularly relevant to its use as a root canal irrigant.

**Clinical Pearl / High-Yield Fact**
When using chlorhexidine as a root canal irrigant, it is essential to note that its antimicrobial activity can be enhanced when used in combination with other irrigants, such as sodium hypochlorite. Additionally, chlorhexidine's potential for tissue staining and discoloration should be taken into account when selecting a root canal irrigant.

✓ Correct Answer: D. All of the above