**Core Concept**
Anaesthetic death rate is a critical indicator of the quality of care provided in an operating room. A death rate greater than 1 in 100,000 (1:100,000) is considered a threshold for scrutiny of staff or equipment, as it may indicate a systemic issue or inadequate safety protocols.

**Why the Correct Answer is Right**
The correct answer is based on the principle of "near misses" and "adverse events" in anaesthesia. A death rate of 1:100,000 is considered a benchmark for a safe anaesthesia practice. This threshold is derived from the National Health Service (NHS) guidelines and is widely accepted in the medical community. It is essential to investigate any deaths above this threshold to identify the underlying causes and implement corrective measures to prevent similar events in the future.

**Why Each Wrong Option is Incorrect**
* **Option A:** 0.1% (1:1000) is still within the acceptable range for anaesthesia mortality, as it is below the threshold for scrutiny.
* **Option B:** 0.01% (1:10,000) is also within the acceptable range, as it is significantly lower than the threshold for scrutiny.
* **Option C:** 0.001% (1:100,000) is the correct threshold for scrutiny, as it is the benchmark for a safe anaesthesia practice.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that anaesthesia mortality rates can be influenced by various factors, including the type of surgery, patient demographics, and anaesthesia technique. A death rate above the threshold should prompt a comprehensive investigation to identify the underlying causes and implement corrective measures to prevent similar events in the future.

**Correct Answer: . 1:100,000**