**Core Concept**
The question is testing knowledge of a specific toxin's lethal dose, which is a critical concept in toxicology. Understanding the lethal dose of a poison is essential for diagnosing and managing poisoning cases.

**Why the Correct Answer is Right**
The correct answer is related to digoxin, a cardiac glycoside used in the treatment of heart failure and atrial fibrillation. Digoxin works by inhibiting the Na+/K+-ATPase pump, leading to an increase in intracellular sodium and calcium concentrations, which enhances cardiac contractility. However, excessive digoxin levels can lead to digitalis toxicity, characterized by symptoms such as nausea, vomiting, confusion, and arrhythmias. The lethal dose of digoxin is typically considered to be around 10-15 mg in adults.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the correct toxin. Without knowing the toxin, it is impossible to accurately determine the lethal dose.
**Option B:** This option is incorrect because it is not a specific enough answer. While it may be a close estimate, it does not provide a precise answer, and the question is looking for a specific value.
**Option C:** This option is incorrect because it is not the correct lethal dose of digoxin. The correct answer is a more specific value.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the lethal dose of digoxin can vary significantly depending on factors such as age, weight, and renal function. Additionally, digoxin toxicity can be challenging to diagnose, and a high index of suspicion is necessary to avoid missing the diagnosis.

**Correct Answer: C. 10-15 mg.**