**Core Concept**
Tetracaine is a long-acting local anesthetic (L.A) agent used for topical application and spinal anesthesia. It belongs to the ester group of local anesthetics, which are metabolized by plasma cholinesterases.

**Why the Correct Answer is Right**
Tetracaine is the longest-acting local anesthetic among the options, with a duration of action of approximately 12-18 hours. This is due to its high lipid solubility, which allows it to bind to nerve tissue for an extended period. Tetracaine's long duration of action makes it suitable for procedures requiring prolonged anesthesia, such as spinal anesthesia for major surgeries.

**Why Each Wrong Option is Incorrect**
**Option A:** Bupivacaine is a long-acting local anesthetic, but its duration of action (4-6 hours) is shorter than tetracaine's.
**Option C:** Xylocaine (lidocaine) has a moderate duration of action (1-2 hours) and is not considered long-acting.
**Option D:** Procaine is a short-acting local anesthetic with a duration of action of approximately 30-60 minutes.

**Clinical Pearl / High-Yield Fact**
Tetracaine's long duration of action can lead to systemic toxicity, including central nervous system and cardiovascular effects. Therefore, it is essential to use tetracaine with caution and monitor patients closely during procedures requiring its use.

✓ Correct Answer: B. Tetracaine