**Core Concept**
Cytochrome C oxidase is a crucial enzyme in the mitochondrial electron transport chain, responsible for transferring electrons from cytochrome C to molecular oxygen, generating a proton gradient that drives ATP synthesis. The enzyme's activity is essential for maintaining cellular energy homeostasis.

**Why the Correct Answer is Right**
The electron flow in Cytochrome C oxidase can be blocked by cyanide (CN-), a potent inhibitor that binds to the iron atom within the enzyme's active site. This binding disrupts the enzyme's ability to transfer electrons to oxygen, effectively halting the electron transport chain and ATP synthesis. Cyanide's high affinity for Cytochrome C oxidase makes it an effective poison, as it can rapidly inhibit cellular respiration.

**Why Each Wrong Option is Incorrect**
**Option A:** Azide (N3-) is a competitive inhibitor of Cytochrome C oxidase, but it is not as potent as cyanide and has a different mechanism of action.
**Option B:** Rotenone is an inhibitor of Complex I (NADH dehydrogenase) in the electron transport chain, not Cytochrome C oxidase.
**Option C:** Antimycin A is an inhibitor of Complex III (cytochrome b-c1 complex) in the electron transport chain, not Cytochrome C oxidase.

**Clinical Pearl / High-Yield Fact**
Cyanide poisoning is a medical emergency that requires immediate treatment, often involving the administration of hydroxocobalamin, a cyanide antidote that binds to and neutralizes the toxin.

**Correct Answer: C. Cyanide**