**Core Concept**
Lithium is a mood stabilizer used in the treatment of bipolar disorder. Its pharmacokinetics, particularly its half-life, play a crucial role in determining dosing intervals and maintaining therapeutic levels in the body.

**Why the Correct Answer is Right**
Lithium's half-life is approximately 24 hours, which means that it takes about 24 hours for the concentration of lithium in the blood to reduce by half. This relatively long half-life allows for once- or twice-daily dosing, making it a convenient option for patients. Lithium's half-life is influenced by factors such as age, weight, and renal function, but a typical half-life of 24 hours is generally accepted.

**Why Each Wrong Option is Incorrect**
**Option A:** 8 hours - This is too short for lithium's half-life, which would require more frequent dosing and may lead to toxicity.

**Option B:** 16 hours - While closer to the correct answer, this is still shorter than the actual half-life of lithium.

**Option D:** 36 hours - This is longer than the typical half-life of lithium, which may lead to accumulation and increased risk of toxicity.

**Clinical Pearl / High-Yield Fact**
It's essential to monitor lithium levels regularly, especially in patients with renal impairment, as lithium clearance is reduced in such cases. A lithium level of 0.8-1.2 mmol/L is generally considered therapeutic.

**✓ Correct Answer: C. 24 hours**