## Core Concept
Sporicidal disinfectants are chemical agents capable of killing bacterial spores. These are critical in high-level disinfection and sterilization processes, particularly in healthcare settings to prevent the transmission of infections.

## Why the Correct Answer is Right
Glutaraldehyde is a well-known sporicidal disinfectant used for sterilizing medical and dental equipment that cannot be sterilized by heat. Ortho-phthalaldehyde (OPA) and hydrogen peroxide are also recognized for their sporicidal properties. In contrast, chlorhexidine is primarily an antiseptic and disinfectant effective against a wide range of bacteria and viruses but is not reliably sporicidal.

## Why Each Wrong Option is Incorrect
* **Option A:** Glutaraldehyde is indeed sporicidal, making it incorrect as an "except" answer.
* **Option B:** Ortho-phthalaldehyde (OPA) exhibits sporicidal activity, which eliminates it as the correct "except" choice.
* **Option C:** Hydrogen peroxide, especially in higher concentrations, has sporicidal properties, so it's not the correct answer.

## Why Option D is Correct
* **Option D:** Chlorhexidine, while useful as an antiseptic and for skin disinfection, does not reliably kill bacterial spores, making it the correct "except" in the context of sporicidal disinfectants.

## Clinical Pearl / High-Yield Fact
A key point to remember is that not all disinfectants are sporicidal. Chlorhexidine, commonly found in skin preparations and mouthwashes, is not effective against bacterial spores, which is a critical distinction in infection control.

## Correct Answer: D. Chlorhexidine.