**Core Concept**
Capnography is a monitoring technique that measures the concentration of carbon dioxide (CO2) in exhaled breath. This is particularly useful in the context of anesthesia, where it can provide valuable information about the patient's respiratory status and the proper placement of endotracheal tubes.

**Why the Correct Answer is Right**
The correct answer is C, as capnography is essential for verifying the correct placement of endotracheal tubes. When an endotracheal tube is correctly positioned in the trachea, capnography will detect a characteristic waveform, indicating the presence of CO2 in the exhaled breath. This waveform is absent when the tube is misplaced, such as in the esophagus. The correct placement of the endotracheal tube is crucial for ensuring adequate ventilation and preventing complications like aspiration.

**Why Each Wrong Option is Incorrect**
**Option A:** Determining Vaporizer malfunction or contamination is not a primary use of capnography. Vaporizer malfunction is typically detected through monitoring of anesthetic agent delivery and patient response.
**Option B:** Determining circuit hypoxia is not directly related to capnography. Hypoxia is usually detected through pulse oximetry or arterial blood gas analysis.
**Option D:** Detecting the concentration of oxygen in the anesthetic circuit is not a function of capnography, which specifically measures CO2 levels.

**Clinical Pearl / High-Yield Fact**
A key clinical application of capnography is the "capnogram," which is a graphical representation of CO2 concentration over time. The presence of a characteristic "downslope" in the capnogram indicates the correct placement of the endotracheal tube.

**✓ Correct Answer: C. Determining the appropriate placement of endotracheal tube.**