Which cyanide is most poisonous potassium cyanide hydrogen cyanide?

The most deadliest poison would have to be the toxins released by certain bacteria in the Clostridium genus. Botulinum toxin is a serious neurotoxin that disables motor nerves' abilities to release acetylchloline, which is the neurotransmitter that relays nerve signals to muscles, and paralysis occurs. As this progresses the muscles that control the airway and breathing fail. The Botulinun toxin is by far the most deadliest poison. If you were to have the same amount of this poison as there is in a snake bite you could end an entire city.