**Core Concept**
The half-life of T3 (triiodothyronine) is an essential concept in endocrinology, referring to the time required for the concentration of T3 in the blood to decrease by half through metabolic processes. T3 is a thyroid hormone that plays a crucial role in regulating metabolism, growth, and development.

**Why the Correct Answer is Right**
The half-life of T3 is approximately 2 days, which is relatively short compared to other thyroid hormones like thyroxine (T4), which has a half-life of around 6-7 days. This shorter half-life allows T3 to rapidly regulate metabolic processes in response to changes in the body's needs. T3 is converted from T4 in the peripheral tissues through the action of the enzyme 5'-deiodinase, which is responsible for the rapid metabolism of T3.

**Why Each Wrong Option is Incorrect**
* **Option A:** 10 hours is too short to be the half-life of T3, as it would imply an extremely rapid metabolism.
* **Option C:** 6 days is the half-life of T4, not T3, which is a distinct thyroid hormone with a different metabolic profile.
* **Option D:** 10 days is an excessively long half-life for T3, which would suggest an impaired metabolic process.

**Clinical Pearl / High-Yield Fact**
The conversion of T4 to T3 in peripheral tissues is a critical step in regulating thyroid hormone activity, and any impairment in this process can lead to changes in metabolic function and clinical symptoms.

✓ Correct Answer: B. 2 day