**Core Concept**
Disinfection by autoclaving is a process used to eliminate microorganisms from non-living materials. Autoclaving involves subjecting the items to high pressure steam at a temperature of 121°C for a specified duration. This method is effective against a broad spectrum of microorganisms, including bacteria, viruses, and fungi.

**Why the Correct Answer is Right**
Sharp instruments, such as scalpels, needles, and knives, are not recommended for autoclaving due to the potential for damage to the instrument's cutting edge or the introduction of microorganisms into the instrument's crevices. Autoclaving can also cause the instruments to become brittle or discolored. Therefore, sharp instruments are typically sterilized using dry heat sterilization or chemical sterilization methods, such as ethylene oxide gas.

**Why Each Wrong Option is Incorrect**
**Option A:** Sputum is a potentially infectious material and can be effectively disinfected by autoclaving. Autoclaving is a reliable method for eliminating microorganisms from sputum.
**Option B:** Linen can be disinfected by autoclaving, making it a suitable option for items that require high-level disinfection.
**Option D:** Glass syringes can be safely autoclaved without risk of damage or contamination.

**Clinical Pearl / High-Yield Fact**
When handling sharp instruments, it is essential to use proper handling and storage techniques to prevent injuries and maintain sterility. Always use a secure storage container and label the instrument as "Sharp" or "Biohazard" to alert others to potential risks.

**✓ Correct Answer: C. Sharp instrument**