**Core Concept**
Pre-anaesthetic medication refers to the administration of drugs prior to anaesthesia to reduce anxiety, prevent nausea and vomiting, and facilitate endotracheal intubation. These medications can be divided into various categories, including anxiolytics, anticholinergics, and opioids.

**Why the Correct Answer is Right**
Succinyl choline is a depolarizing muscle relaxant commonly used to induce muscle paralysis during endotracheal intubation. It is not typically used in pre-anaesthetic medication due to its potential to cause muscle fasciculations, bradycardia, and hyperkalemia. **Option D** is incorrect because succinyl choline is not a pre-anaesthetic medication; rather, it is used during the induction of anaesthesia to facilitate endotracheal intubation.

**Why Each Wrong Option is Incorrect**
**Option A:** Diazepam is a benzodiazepine that can be used in pre-anaesthetic medication to reduce anxiety and promote sedation.
**Option B:** Scopolamine is an anticholinergic agent that can be used to prevent bradycardia and reduce salivation during anaesthesia.
**Option C:** Morphine is an opioid analgesic that can be used in pre-anaesthetic medication to reduce anxiety and provide pain relief.

**Clinical Pearl / High-Yield Fact**
When selecting pre-anaesthetic medications, it is essential to consider the patient's medical history, including any allergies, respiratory problems, or cardiovascular disease. Additionally, the choice of medication should take into account the type of surgery and the anaesthetic technique to be used.

**✓ Correct Answer: D. Succinyl choline. It is not commonly used in pre-anaesthetic medication.**