Ans. D: Blocks Cytochrome enzyme P- 450Cyanide poisoning occurs when a living organism is exposed to a compound that produces cyanide ions (CN-) when dissolved in water. Common poisonous cyanide compounds include hydrogen cyanide gas and the crystalline solids potassium cyanide and sodium cyanide.The cyanide ion halts cellular respiration by inhibiting an enzyme in mitochondria called cytochrome c oxidase.