Which of the following disease is caused by protozoan?

Malaria

The correct answer is Option (3) →Malaria

Malaria is caused by a protozoan parasite belonging to the genus Plasmodium. The most common species that cause malaria in humans are Plasmodium falciparum, Plasmodium vivax, Plasmodium ovale, and Plasmodium malariae. The disease is transmitted by the bite of an infected female Anopheles mosquito.

Other options are incorrect because:

• Common cold is caused by a virus, most commonly rhinoviruses.
• Typhoid is caused by a bacterium, Salmonella typhi.
• AIDS is caused by the HIV virus (Human Immunodeficiency Virus).

Therefore, the correct answer is malaria, which is caused by a protozoan parasite.