The correct answer for the question is Option 2: protozoa. Malarial parasite is caused by the protozoan parasite Plasmodium. Protozoa are single-celled organisms that belong to the kingdom Protista. They are eukaryotic organisms, which means they have a true nucleus and membrane-bound organelles.

Protozoa are distinct from other microorganisms like bacteria, viruses, and fungi. Bacteria are prokaryotic organisms, which means they lack a true nucleus and membrane-bound organelles. Viruses are not considered living organisms as they cannot reproduce on their own and require a host cell to multiply. Fungi, on the other hand, are eukaryotic organisms, but they are multi-celled and have cell walls made of chitin, while protozoa are single-celled and lack cell walls.

Therefore, the malarial parasite is a protozoan parasite, specifically the Plasmodium parasite, which causes the disease malaria. It is important to understand the characteristics and classifications of different microorganisms to better understand their roles in diseases and treatment options.