**Core Concept**
Phase II block, also known as the "depolarizing block," is a type of neuromuscular blockade characterized by a rapid onset and short duration. It occurs when a drug depolarizes the motor endplate, leading to muscle contraction followed by prolonged depolarization and paralysis.

**Why the Correct Answer is Right**
The correct answer is a depolarizing neuromuscular blocking agent that works by mimicking acetylcholine at the neuromuscular junction, causing initial muscle contraction (phase I) followed by prolonged depolarization and paralysis (phase II). This drug binds to the nicotinic acetylcholine receptor, causing a conformational change that leads to sustained depolarization and muscle paralysis.

**Why Each Wrong Option is Incorrect**
**Option A:** This is incorrect because it is a non-depolarizing neuromuscular blocking agent, which acts by competitively blocking acetylcholine receptors at the neuromuscular junction, leading to prolonged depolarization and paralysis without initial muscle contraction.

**Option B:** This is incorrect because it is a succinylcholine-like drug, but it is actually a non-depolarizing agent that works by blocking acetylcholine receptors at the neuromuscular junction.

**Option C:** This is incorrect because it is a non-depolarizing neuromuscular blocking agent that works by competitively blocking acetylcholine receptors at the neuromuscular junction, leading to prolonged depolarization and paralysis without initial muscle contraction.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that depolarizing neuromuscular blocking agents, like the correct answer, can cause muscle fasciculations (twitching) before inducing paralysis, which can be a useful clinical sign to differentiate them from non-depolarizing agents.

**Correct Answer:** C. Succinylcholine.