What is the prepositional phrase in sentence Do you know about value of milk?

The prepositional phrase in the sentence "Do you know about the value of milk?" is "of milk".

Here's why:

* Prepositional phrases start with a preposition (in this case, "of") and end with a noun or pronoun (in this case, "milk").

* Prepositions show the relationship between the noun/pronoun and the rest of the sentence. Here, "of" tells us that "milk" is the object of the "value."