**Core Concept**
Skeletal muscle relaxants are a class of medications used to relieve muscle spasms and pain. Some of these medications can cause pain on injection, which is a significant side effect that clinicians should be aware of.

**Why the Correct Answer is Right**
The correct answer is **Vecuronium**. Vecuronium is a non-depolarizing neuromuscular blocking agent that is commonly used in anesthesia to facilitate endotracheal intubation and to provide muscle relaxation during surgery. Vecuronium causes pain on injection due to its local anesthetic properties. When vecuronium is administered intravenously, it can cause a burning sensation, which is a result of its action on the nerve endings.

**Why Each Wrong Option is Incorrect**
* **Option A: Pancuronium**. Pancuronium is another non-depolarizing neuromuscular blocking agent, but it does not typically cause pain on injection. Pancuronium has a longer duration of action compared to vecuronium and is often used for longer surgical procedures.
* **Option B: Rocuronium**. Rocuronium is a non-depolarizing neuromuscular blocking agent that is known for its rapid onset of action. While rocuronium can cause histamine release, leading to side effects such as hypotension and flushing, it does not typically cause pain on injection.
* **Option C: Succinylcholine**. Succinylcholine is a depolarizing neuromuscular blocking agent that is commonly used for rapid sequence intubation. Succinylcholine can cause muscle fasciculations and can also cause histamine release, but it does not typically cause pain on injection.

**Clinical Pearl / High-Yield Fact**
It's essential to note that vecuronium's pain on injection can be mitigated by administering it slowly and mixing it with a large volume of saline solution. This can help reduce the burning sensation associated with vecuronium administration.

**Correct Answer:** C. Vecuronium