## **Core Concept**
The half-life of a radioactive substance is the time required for half of the initial amount of the substance to decay. Iodine-131 is a radioactive isotope commonly used in medical treatments and diagnostic procedures.

## **Why the Correct Answer is Right**
Iodine-131 has a well-established half-life, which is crucial for calculating the dosage and duration of its therapeutic effects. The correct half-life of Iodine-131 is approximately 8 days. This duration allows for its effective use in treating thyroid disorders, including thyroid cancer, without causing undue harm to the patient.

## **Why Each Wrong Option is Incorrect**
- **Option A:** 2 days - This is too short for the half-life of Iodine-131.
- **Option B:** 6 days - While close, it is still not the accurate half-life of Iodine-131.
- **Option D:** 10 days - This is slightly longer than the actual half-life.

## **Clinical Pearl / High-Yield Fact**
A key clinical consideration for Iodine-131 therapy is its half-life and how it influences the duration of treatment and potential side effects. For example, patients often need to isolate themselves for a period after treatment to minimize radiation exposure to others.

## **Correct Answer:** C. 8 days.