**Core Concept**
Irreversible cell injury occurs when cellular damage is so severe that the cell can no longer maintain homeostasis and eventually undergoes cell death. This type of injury is often caused by prolonged exposure to toxins, lack of oxygen, or severe cellular stress.

**Why the Correct Answer is Right**
Irreversible cell injury is characterized by the loss of membrane integrity, rupture of lysosomes, and activation of various cellular enzymes that lead to cell death. The cell's ability to maintain its internal environment is compromised, and the cell undergoes necrosis or apoptosis. This process is often irreversible and can lead to tissue damage and organ dysfunction.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because reversible cell injury is a type of cellular damage that can be repaired by the cell itself, whereas irreversible injury is more severe and leads to cell death.

**Option B:** This option is incorrect because apoptosis is a type of programmed cell death that can be a form of cell injury, but it is not the same as irreversible injury.

**Option C:** This option is incorrect because necrosis is a form of cell death, but it is not the same as irreversible injury. Necrosis can occur due to various causes, including infection, toxins, or trauma.

**Option D:** This option is incorrect because cellular adaptation is a process by which cells respond to changes in their environment, but it is not a form of cell injury.

**Clinical Pearl / High-Yield Fact**
It's essential to note that reversible cell injury can often be prevented or reversed with prompt treatment, whereas irreversible injury can lead to long-term tissue damage and organ dysfunction.

**Correct Answer:** C. Necrosis.