Which order is correct?
- How much milk is in the fridge left?
- How much milk is left in the fridge?
This is an interesting question, because it depends how you interpret the sentence. What is the object? If you think it is
How much milk is in the fridge?
Then modified by left, I can see where there would be confusion. However, it's actually:
How much milk is left?
Modified by in the fridge. The idea of something "being left" is pretty much a set phrase that can be treated as a phrasal verb, though I believe it's really a passive construction using to leave in the same sense as "he left her at the station". Thus, it is in the fridge that comes last.
Now, milk in the fridge can be used as a noun phrase, so you could grammatically say:
How much milk in the fridge is left?
But a native speaker never would say that. It's always:
How much milk is left in the fridge?