**Core Concept**
Sterilization of fibre optic instruments requires a method that effectively kills all microorganisms, including bacteria, viruses, and fungi, without damaging the delicate equipment. This is particularly challenging due to the sensitive nature of fibre optic technology.

**Why the Correct Answer is Right**
Ethylene oxide (ETO) is widely used for sterilizing fibre optic instruments, including endoscopes. ETO is a potent bactericidal and virucidal agent that penetrates packaging and reaches all surfaces, including those with complex geometries. It is effective against a broad spectrum of microorganisms and is commonly used in medical device sterilization. The use of ETO for fibre optic instruments is preferred due to its ability to maintain the structural integrity of the delicate components.

**Why Each Wrong Option is Incorrect**
**Option A:** Glutaraldehyde is a disinfectant commonly used for sterilizing heat-sensitive equipment, but it is not suitable for fibre optic instruments due to its potential to damage the optical components. Additionally, glutaraldehyde requires a longer exposure time and higher concentrations than ETO.
**Option B:** Hydrogen peroxide is a disinfectant used for sterilizing medical equipment, but it is not the preferred choice for fibre optic instruments. Hydrogen peroxide can be corrosive and may damage the sensitive components of fibre optic instruments.
**Option C:** Autoclaving is a method of sterilization that uses high-pressure steam to kill microorganisms. However, it is not suitable for fibre optic instruments due to the risk of damage from high temperatures and steam.

**Clinical Pearl / High-Yield Fact**
When sterilizing fibre optic instruments, it is essential to follow the manufacturer's instructions and guidelines to ensure effective sterilization without damaging the equipment. This includes using the correct sterilizing agent, exposure time, and concentration.

**Correct Answer:** C. Ethylene oxide.