It is most difficult to prepare drugs against

1. bacteria
2. virus
3. protozoa
4. fungi

Correct Answer: (b) virus

Explanation:

It's very difficult to prepare drugs against viruses because antibiotic types of drugs cannot kill viruses.  Antibiotics are programmed to attack the cell wall of bacteria, while viruses don't have cell walls that can be attacked by antibiotics. Instead, they are covered by a protective protein coat.

Outside the body of the host organisms, the viruses become nonliving. Viruses can't reproduce on their own, rather they attach themselves to healthy cells of the body. Once it enters the host cell, they reproduce and make copies of themselves.

Although vaccines and antiviral medications can slow down the reproductive cycle of the virus, the property of the viruses undergoes repetitive mutation form new strains which show resistance towards the developed vaccine.