The correct answer is option 3: Green plants. Green plants are the largest fixators of solar energy. They have a pigment called chlorophyll that allows them to capture sunlight and convert it into chemical energy through the process of photosynthesis. During photosynthesis, plants use solar energy to combine carbon dioxide and water to produce glucose and oxygen. This glucose is then used by plants for energy and growth, while oxygen is released into the atmosphere. Green plants play a vital role in the ecosystem as they not only produce food for themselves but also provide energy for other organisms in the food chain. Bacteria, fungi, and protozoa do not possess the same level of photosynthetic capabilities as green plants, making option 3 the correct answer.