**Core Concept:** Local anaesthetics are a class of drugs that are used to temporarily block nerve conduction by inhibiting voltage-gated sodium channels in neurons, thereby preventing the transmission of pain signals.

**Why the Correct Answer is Right:** The correct answer, **D**: Chloroform, is a historical anaesthetic used in the early days of anaesthesia before the development of local anaesthetics. Chloroform is a volatile, unspecific anaesthetic agent, which works by diffusing through the lipid membrane of neurons and disrupting various cellular processes, leading to loss of sensation and consciousness.

**Why Each Wrong Option is Incorrect:**

A. **Option A (Ether):** Ether is also a volatile anaesthetic agent, similar to Chloroform. However, it is more unpredictable and has a higher risk of causing cardiac toxicity, which led to its discontinuation in clinical practice.

B. **Option B (Sodium Bicarbonate):** Sodium bicarbonate is a buffer used to neutralize acidic substances and maintain pH balance. It is not a local anaesthetic.

C. **Option C (Lidocaine):** Lidocaine is a local anaesthetic, commonly used for peripheral nerve blocks and epidural anaesthesia. It works by blocking voltage-gated sodium channels, preventing nerve impulse transmission.

**Clinical Pearl:** The correct answer, Chloroform, is no longer used in clinical practice due to its unpredictable effects and higher risk of cardiac toxicity. Local anaesthetics, such as Lidocaine, are the preferred choice for pain management due to their targeted and safer effects on nerve conduction.