**Core Concept**
Technetium-99m (Tc-99m) is a metastable nuclear isomer used extensively in nuclear medicine for diagnostic imaging due to its favorable properties, including a suitable half-life, gamma radiation, and low cost.

**Why the Correct Answer is Right**
The half-life of Tc-99m is approximately 6 hours, which allows for adequate imaging time and facilitates the use of this isotope in various medical applications. This is crucial for clinical imaging, as it enables the collection of high-quality images without exposing patients to excessive radiation. The short half-life of Tc-99m also reduces the risk of radiation exposure to medical staff and the environment.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect, as the half-life of Tc-99m is not 2 hours. This option is a common distractor, as some students may mistakenly recall the half-life of other isotopes or confuse Tc-99m with I-131, which has a significantly longer half-life.

**Option B:** Incorrect, as the half-life of Tc-99m is not 1 hour. This option is another distractor, as some students may incorrectly recall the half-life of other isotopes or confuse Tc-99m with other short-lived isotopes.

**Option D:** Incorrect, as the half-life of Tc-99m is not 24 hours. This option is a distractor, as some students may mistakenly recall the half-life of other isotopes or confuse Tc-99m with isotopes used in longer-term applications.

**Clinical Pearl / High-Yield Fact**
The half-life of Tc-99m is a critical parameter in nuclear medicine, and understanding its value is essential for selecting the appropriate radiopharmaceutical for diagnostic imaging.

**Correct Answer: C. 6 hours**