**Core Concept**
Cell injury can be reversible or irreversible, depending on the severity and duration of the insult. Reversible cell injury occurs when the cell's energy stores are depleted, but the cell membrane remains intact. In contrast, irreversible cell injury occurs when the cell membrane is damaged, leading to cell death.

**Why the Correct Answer is Right**
Calcium overload is a key mechanism in producing irreversible cell injury faster. When the cell membrane is damaged, calcium ions flood into the cell, triggering a cascade of events that ultimately lead to cell death. This is because calcium activates various enzymes and pathways that disrupt cellular homeostasis and lead to cell lysis. In particular, calcium activates phospholipase A2, which hydrolyzes phospholipids in the cell membrane, leading to its degradation.

**Why Each Wrong Option is Incorrect**
**Option A:** Ischemia alone can cause reversible cell injury if the oxygen supply is restored promptly. However, if ischemia is prolonged, it can lead to irreversible cell injury.
**Option B:** Coagulative necrosis is a type of irreversible cell injury, but it is not the fastest mechanism. Coagulative necrosis occurs in response to ischemia, infection, or trauma, and it takes longer to develop than other forms of cell injury.
**Option C:** Liquefactive necrosis is also a type of irreversible cell injury, but it is typically associated with enzymatic digestion of the cell, such as in bacterial infections. This process is slower than calcium overload.

**Clinical Pearl / High-Yield Fact**
Remember the "4Ds" of cell injury: Damage (ischemia, toxins), Depletion (energy stores), Distortion (cell membrane damage), and Death (irreversible cell injury).

**Correct Answer: C. Calcium overload is a key mechanism in producing irreversible cell injury faster.**