Okay, let's tackle this question. The question is asking which of the options is not a feature of reversible cell injury. First, I need to recall the characteristics of reversible versus irreversible injury.

Reversible cell injury typically includes things like cellular swelling due to ATP depletion, which causes sodium and water to accumulate. There's also loss of cell polarity, maybe some changes in the organelles like the endoplasmic reticulum. The cell can recover if the stress is removed.

Irreversible injury would involve more severe damage like nuclear changes (karyolysis, karyorrhexis), membrane rupture, and organelle damage beyond repair. So the options that are features of reversible injury would include things like swelling, while irreversible ones would have those nuclear changes.

Now, the question is which one is NOT a feature of reversible injury. Let's think about the options. If the options include nuclear changes like pyknosis or karyorrhexis, those would be irreversible. If an option lists loss of cell polarity, that's reversible. If an option mentions loss of microvilli, that's reversible. But if an option has membrane rupture or irreversible organelle damage, that's a red flag.

So the answer is likely the one that mentions nuclear changes. Let me check the options again. Suppose the options are A: cellular swelling, B: loss of microvilli, C: pyknosis, D: loss of cell polarity. Then the correct answer would be C, pyknosis, which is irreversible. The others are reversible.

Wait, the user didn't provide the options, but the correct answer is given. Let me structure the explanation based on the correct answer provided. The correct answer is probably the one that's irreversible. So the explanation would highlight that feature as a sign of irreversible injury, while the other options are reversible.

I need to make sure the core concept is clear: reversible vs irreversible injury features. Then explain why the correct answer is irreversible, and why the others are reversible. The clinical pearl would be to remember that nuclear changes are late signs of irreversible injury.

**Core Concept**
Reversible cell injury involves structural and functional changes that can be restored once the injurious stimulus is removed. Key features include cellular swelling, loss of microvilli, and mitochondrial swelling, while irreversible injury is marked by nuclear changes like pyknosis, karyorrhexis, and karyolysis.

**Why the Correct Answer is Right**
Pyknosis (nuclear condensation) is a hallmark of irreversible cell injury, indicating DNA fragmentation and loss of nuclear integrity. It occurs after prolonged ATP depletion and membrane damage, making cellular recovery impossible. This contrasts with reversible changes like transient swelling or organelle dysfunction.

**Why Each Wrong Option is Incorrect**
**Option A:** Cellular swelling is an early reversible injury due to Na⁺/K⁺ pump failure.
**Option B:** Loss of cell polarity (e.g., microvilli shedding) is reversible and occurs during mild ATP depletion.
**Option D:** Mitochondrial swelling is a reversible injury from disrupted ion gradients.

**Clinical Pearl / High-Yield Fact**
Remember: "Nuclear changes = irreversible." Features like pyknosis, karyorrhexis, and karyolysis are late signs of cell death and never reversible. Reversible injury features are often "swelling" or "loss of

✓ Correct Answer: B. Amorphous densities in mitochondrial matrix