Answer: Kingdom Plantae
According to Karina's observation, the organism has many cells it means it is a multicellular organism. Each cell with a cell wall and green chloroplast it means it may belong to plant kingdom as all the cells of plants have cell wall and they have green chloroplast which contains chlorophyll to capture sunlight to conduct photosynthesis. It has a nucleus and membrane bound organelles, these are found in plants, animals and fungi groups. All features observed in the organism are indicating those which are commonly found in plants. Therefore, this organism will be classified in Kingdom Plantae.