Potassium cyanide is the chemical substance used for making rat poison. Rat poison, also known as rodenticide, is a substance used to kill rats and other rodents. It is typically formulated with toxic chemicals that are attractive to rodents but deadly when ingested.

Potassium cyanide is a highly toxic compound that is commonly used in rat poison due to its lethal effects on rodents. Here is an explanation of why potassium cyanide is used as a rat poison:

Properties of Potassium Cyanide:
- Potassium cyanide (KCN) is a white, crystalline solid that is highly soluble in water.
- It is an inorganic compound with the chemical formula KCN.
- Potassium cyanide is a powerful poison due to its ability to disrupt cellular respiration, leading to severe metabolic dysfunction and ultimately death.

Mode of Action:
- Potassium cyanide is a potent inhibitor of the enzyme cytochrome c oxidase, which is vital for the electron transport chain in cellular respiration.
- By inhibiting cytochrome c oxidase, potassium cyanide disrupts the production of adenosine triphosphate (ATP), the main energy source for cells.
- Without ATP production, cells cannot carry out their normal functions, leading to organ failure and death.

Effect on Rodents:
- Rodents, including rats, have a similar cellular respiration process as humans and other mammals.
- When rodents ingest potassium cyanide, it rapidly enters their bloodstream and inhibits cytochrome c oxidase in their cells.
- As a result, the rodents experience severe metabolic dysfunction, leading to organ failure and death.

Safety Considerations:
- Potassium cyanide is not only toxic to rats but also highly toxic to humans and other animals.
- It is a controlled substance due to its potential for misuse and lethality.
- Handling potassium cyanide requires strict safety measures, protective clothing, and proper disposal procedures to prevent accidental poisoning and environmental contamination.

In conclusion, potassium cyanide is the chemical substance used for making rat poison due to its potent inhibition of cellular respiration, which leads to severe metabolic dysfunction and ultimately death in rodents. However, it is essential to handle this toxic compound with extreme caution due to its high toxicity to humans and other animals.