Introduction:
Antipyretics are drugs that are used to reduce fever. They work by blocking the production of prostaglandins in the brain that are responsible for raising the body's temperature.

Answer:
C) Barbituric acid is not an antipyretic.

Explanation:
Barbituric acid is not an antipyretic because it is a type of sedative that is used to treat anxiety and insomnia. It has no effect on reducing fever.

On the other hand, Aspirin, Paracetamol, and Phenacetin are antipyretics.

1. Aspirin - It is a nonsteroidal anti-inflammatory drug (NSAID) that is used to treat fever, pain, and inflammation. It works by blocking the production of prostaglandins, which are responsible for causing fever and inflammation.

2. Paracetamol - It is an analgesic and antipyretic drug that is used to treat fever and pain. It works by blocking the production of prostaglandins in the brain that cause fever and pain.

3. Phenacetin - It is an analgesic and antipyretic drug that is used to treat fever and pain. It works by blocking the production of prostaglandins in the brain that cause fever and pain. However, it is no longer used due to its side effects.

Conclusion:
In summary, Barbituric acid is not an antipyretic drug, whereas Aspirin, Paracetamol, and Phenacetin are antipyretic drugs that are used to treat fever and pain.

Antipyretic means they reduce fever. So barbituric acid is pain killer or sleeping agent so it is not antipyretic