**Core Concept**
Local anaesthetics are a class of drugs used to block the sensation of pain in a specific area of the body. They work by inhibiting the conduction of nerve impulses, which prevents the transmission of pain signals to the brain. The duration of action of local anaesthetics is influenced by their lipid solubility, protein binding, and the presence of esterases that metabolize them.

**Why the Correct Answer is Right**
Dibucaine is a long-acting local anaesthetic that has a duration of action that can last up to 12 hours. This is due to its high lipid solubility, which allows it to penetrate the nerve sheath and bind to the sodium channels for an extended period. Additionally, dibucaine has a low affinity for plasma proteins, which also contributes to its prolonged action. Dibucaine's mechanism of action involves the inhibition of sodium channels, which prevents the depolarization of nerve cells and the transmission of pain signals.

**Why Each Wrong Option is Incorrect**
**Option A:** Procaine is a short-acting local anaesthetic with a duration of action that lasts only a few minutes. It is rapidly metabolized by plasma cholinesterase, which limits its use to short procedures.
**Option B:** Cocaine is a local anaesthetic with a moderate duration of action, but its use is limited due to its potential for abuse and side effects such as vasoconstriction and tachycardia.
**Option C:** Lidocaine is a medium-acting local anaesthetic with a duration of action that lasts around 1-2 hours. While it is commonly used in clinical practice, it does not have the prolonged action of dibucaine.

**Clinical Pearl / High-Yield Fact**
When choosing a local anaesthetic, consider the duration of action required for the procedure. Short-acting anaesthetics like procaine are suitable for minor procedures, while long-acting anaesthetics like dibucaine are better suited for procedures that require prolonged pain relief.

**✓ Correct Answer: D. Dibucaine**