## Core Concept
The question tests knowledge of radioisotopes and their stability. Radioisotopes are atoms that contain an unstable nucleus and undergo radioactive decay. Stability in radioisotopes is related to the balance of protons and neutrons in the nucleus.

## Why the Correct Answer is Right
The correct answer, , is known for being one of the most stable radioisotopes. It has a half-life of approximately 30.17 years, which is relatively long compared to other radioisotopes. This stability can be attributed to its "magic number" of neutrons (82 neutrons), which is a number that leads to a particularly stable nuclear configuration due to the shell model of the nucleus.

## Why Each Wrong Option is Incorrect
* **Option A:** has a half-life of about 5.26 years, which is significantly shorter than that of . This makes it less stable.
* **Option B:** has a half-life of approximately 8.04 days, indicating it is much less stable than .
* **Option D:** has a half-life of about 2.6 years, which is also much shorter than that of , making it less stable.

## Clinical Pearl / High-Yield Fact
A key point to remember is that radioisotopes with longer half-lives are generally more stable but can pose longer-term health risks due to prolonged exposure to radiation. is used in various medical and industrial applications due to its relatively long half-life and suitable radiation properties.

## Correct Answer Line
**Correct Answer: C.**