The interaction that is most likely to result in the most competition among organisms is:
Grasshoppers and caterpillars eat oak leaves.
This scenario involves two different organisms (grasshoppers and caterpillars) competing for the same resource (oak leaves), which can lead to significant competition. In contrast, the other interactions involve scavengers feeding on leftovers or different types of organisms obtaining light, which may not involve direct competition for the same resource.