The correct answer is option 1: Bacteria. Bacteria are the organisms that reside in the roots of pulse plants to do nitrogen fixation. Nitrogen fixation is the process by which atmospheric nitrogen is converted into a usable form of nitrogen that plants can absorb and utilize for their growth and development.

Option 2: Fungi. Fungi are not involved in nitrogen fixation. Instead, they are known for their role in decomposing organic matter and helping with nutrient recycling in ecosystems.

Option 3: Protozoa. Protozoa are single-celled organisms that are not associated with nitrogen fixation. They are typically found in various habitats, including aquatic environments.

Option 4: Virus. Viruses are not living organisms and cannot perform biological functions like nitrogen fixation. They are parasitic particles that require a host cell to reproduce.

In conclusion, bacteria are the specific organisms that have the ability to reside in the roots of pulse plants and perform nitrogen fixation. They form a symbiotic relationship with the plants, benefiting both parties by providing nitrogen for the plants` growth, while receiving carbohydrates and other nutrients from the plants.