## Core Concept
Iridium-192 (Ir-192) is a radioactive isotope used in various medical and industrial applications, including brachytherapy for cancer treatment. Its radioactive properties make it useful for these purposes. The half-life of a radioactive substance is the time it takes for half of the radioactive atoms in a sample to decay.

## Why the Correct Answer is Right
The half-life of Iridium-192 is approximately 74 days. This duration is critical for applications in brachytherapy, where Ir-192 is used to treat certain types of cancer. The relatively long half-life compared to other radioactive isotopes allows for prolonged treatment periods but also requires careful handling and storage to minimize radiation exposure.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because it does not accurately represent the half-life of Ir-192.
- **Option B:** This option is incorrect because it suggests a half-life that does not match the known properties of Ir-192.
- **Option D:** This option is incorrect because it provides a half-life that is not consistent with the established data for Ir-192.

## Clinical Pearl / High-Yield Fact
A key point to remember is that Ir-192's half-life of approximately 74 days makes it suitable for certain medical applications, particularly in the treatment of cancer. Its use in brachytherapy allows for the delivery of a precise dose of radiation directly to the tumor site.

**Correct Answer: C. 74 days**