The correct answer is option 2. Here`s the explanation:

1. Malaria - E (Blood cells): Malaria is a disease caused by a plasmodium parasite, transmitted through the bite of infected mosquitoes. The parasite is released into the bloodstream.

2. Filaria - D (Lymph node): Filaria is a disease caused by an infection with roundworms. This disease affects the lymph nodes and can cause severe swelling.

3. Encephalitis - B (Brain): Encephalitis is an inflammation of the brain, often due to viral infections.

4. Leukaemia - A (Bone marrow): Leukaemia is a blood cancer that begins in the bone marrow, the soft tissue in the center of the bones, where blood cells are produced.

Therefore, the correct matching is I-E, II-D, III-B, IV-A.

The other options do not match appropriately, as they incorrectly associate diseases with the unrelated parts of the body.