Which of the following is classified as a non-critical instrument?

A mouth mirror is classified as a non-critical instrument because it only comes into contact with intact mucous membranes and does not penetrate or contact blood or other high-risk tissues. Instruments are categorized based on their risk of infection transmission, and non-critical items require less stringent decontamination protocols compared to critical and semi-critical instruments.

Critical instruments, such as surgical scissors and scalpel blades, penetrate soft tissue or bone and carry a high risk of infection, necessitating thorough sterilization after each use. Semi-critical instruments contact mucous membranes and require high-level disinfection. Since a mouth mirror is used primarily for reflecting light and visibility without penetrating tissues, it is safely classified as a non-critical instrument and primarily needs cleaning and low-level disinfection.