If you tagged organic carbon inside a chloroplast with a fluorescent label, the location most likely to have a high concentration of labeled carbon would be in the

The answer is; in the stroma. The chloroplast is the organelle inside the plant cell that performs the process of photosynthesis. Photosynthesis contains two kinds of reactions, the first is the light reactions which happen in the grana as it contains chlorophyll which absorbs light energy. The products of the light reactions are used to fix carbon dioxide in the second reactions which are the dark reactions. The dark reactions happen in the stroma outside the grana. Therefore, the stroma contains more carbon.