**Core Concept**
Beta blockers are a class of medications used to treat various cardiovascular conditions by reducing heart rate, contractility, and blood pressure. However, their use in patients with renal failure requires careful consideration of their pharmacokinetics and potential for exacerbating renal dysfunction.

**Why the Correct Answer is Right**
The correct answer is **C. Labetalol**. Labetalol is a non-selective beta blocker that is metabolized by the liver, but it also undergoes significant renal excretion. In patients with renal failure, the accumulation of labetalol and its active metabolites can lead to exaggerated beta blockade, resulting in hypotension, bradycardia, and potentially life-threatening consequences. Additionally, labetalol's active metabolite, dihydralazine, can cause a further decrease in renal blood flow and glomerular filtration rate (GFR), worsening renal function.

**Why Each Wrong Option is Incorrect**
**Option A:** **Metoprolol** is a selective beta-1 blocker that is primarily excreted unchanged in the urine, but it has a shorter half-life and is less likely to accumulate in patients with renal failure compared to labetalol.

**Option B:** **Nadolol** is a long-acting non-selective beta blocker that is primarily excreted by the liver, making it a safer choice in patients with renal failure.

**Option D:** **Propranolol** is a non-selective beta blocker that is primarily metabolized by the liver, but it has a shorter half-life and is less likely to accumulate in patients with renal failure compared to labetalol.

**Clinical Pearl / High-Yield Fact**
When selecting a beta blocker for patients with renal failure, it is essential to consider the medication's pharmacokinetics, particularly its metabolism and excretion pathways, to minimize the risk of adverse effects.

**Correct Answer:** . C. Labetalol