Answer:
sugar
Step-by-step explanation:
You want to know the middle item, given that rice < sugar and sugar < flour.
When we write the given relations all together, we get ...
rice < sugar < flour
It is pretty clear that the middle item is sugar.
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Additional comment
We can use the < symbol for the left-right ordering, in recognition of the fact that numbers on the left of the symbol are left of numbers on the right of the symbol when they are placed on a number line.
Thus "sugar is right of rice" can be written as "rice < sugar", where "sugar" is on the right side of this symbol.