Find out the alternative which will replace the question mark.
$$138:183::723:?$$

Let's analyze the relationship in the first pair ($138:183$):
The digits of $138$ are rearranged to form $183$. Specifically, the last two digits (tens and units place) are interchanged:

$$1\underline{38}\to 1\underline{83}$$

Applying the exact same rule to the second number ($723$):
Interchange the tens and units digits of $723$:

$$7\underline{23}\to 7\underline{32}$$

Therefore, the missing number is $732$.