**Core Concept**
Local anaesthetics are weak bases that undergo protein binding, which affects their potency and duration of action. Protein binding capacity is a crucial factor in determining the efficacy and potential toxicity of local anaesthetics.

**Why the Correct Answer is Right**
Bupivacaine has the highest protein binding capacity among local anaesthetics. This is because of its lipophilic nature, which allows it to bind strongly to plasma proteins such as albumin. Approximately 8-10% of bupivacaine is bound to plasma proteins, while other local anaesthetics like lidocaine and mepivacaine have lower protein binding capacities. The high protein binding capacity of bupivacaine contributes to its long duration of action and increased potential for toxicity.

**Why Each Wrong Option is Incorrect**
**Option A:** Not specified, but assuming it's a different local anaesthetic, it would not have the highest protein binding capacity.

**Option B:** Actually, bupivacaine is the correct answer, so this option is incorrect by default.

**Option C:** Not specified, but assuming it's a different local anaesthetic, it would not have the highest protein binding capacity.

**Clinical Pearl / High-Yield Fact**
When choosing a local anaesthetic, consider the desired duration of action and the potential for toxicity. Bupivacaine's high protein binding capacity makes it suitable for procedures requiring long-lasting anaesthesia, but its increased potential for toxicity requires careful dosing and monitoring.

**Correct Answer: B. Bupivacaine.**