**Core Concept**
Muscle rigidity is a condition characterized by increased muscle tone and stiffness, often associated with the use of certain anaesthetics or neuromuscular blocking agents. This phenomenon is typically seen in the context of malignant hyperthermia or as a side effect of certain anaesthetic agents.

**Why the Correct Answer is Right**
The correct answer is associated with succinylcholine, a depolarizing neuromuscular blocking agent. Succinylcholine induces muscle rigidity by binding to nicotinic acetylcholine receptors on muscle cells, causing prolonged depolarization and increased muscle tone. This is a result of the drug's action on the nicotinic receptors, which are responsible for transmitting nerve impulses to muscle cells.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the anaesthetic agent associated with muscle rigidity.
**Option B:** This option is incorrect because it is not relevant to the context of muscle rigidity caused by anaesthetics.
**Option C:** This option is incorrect because it is a different class of anaesthetic agent that does not typically cause muscle rigidity.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that succinylcholine-induced muscle rigidity can be a significant concern in patients with certain underlying conditions, such as burns or spinal cord injuries, where increased muscle tone can lead to complications.

**Correct Answer:** A. Succinylcholine.