What is the minimum size for 1 neon tetra? 10 POINTS?

There is no size appropriate for 1 neon tetra because they are schooling fish that should be kept with a mininum of 5 fish and I prefer starting with at least 7. You can keep 7-10 in a 10 gallon aquarium though I don't suggest anything smaller for neons. Another issue is you really should have a well established aquairum before adding neons because they don't imilate to new aquariums well. They just can't handle the cycling of a new aquarium.